diff --git a/src/core/mac/mac.cpp b/src/core/mac/mac.cpp
index 4819f46dc..50073ebc9 100644
--- a/src/core/mac/mac.cpp
+++ b/src/core/mac/mac.cpp
@@ -951,7 +951,6 @@ void Mac::ProcessTransmitSecurity(TxFrame &aFrame)
 
     default:
         OT_ASSERT(false);
-        OT_UNREACHABLE_CODE(break);
     }
 
 #if OPENTHREAD_CONFIG_TIME_SYNC_ENABLE
@@ -1062,7 +1061,6 @@ void Mac::BeginTransmit(void)
 
     default:
         OT_ASSERT(false);
-        OT_UNREACHABLE_CODE(break);
     }
 
 #if OPENTHREAD_CONFIG_TIME_SYNC_ENABLE
@@ -1402,7 +1400,7 @@ void Mac::HandleTransmitDone(TxFrame &aFrame, RxFrame *aAckFrame, Error aError)
 
         aError = mTxError;
     }
-#endif
+#endif // OPENTHREAD_CONFIG_MULTI_RADIO
 
     // Determine next action based on current operation.
 
@@ -1494,14 +1492,14 @@ void Mac::HandleTransmitDone(TxFrame &aFrame, RxFrame *aAckFrame, Error aError)
         Get<DataPollHandler>().HandleSentFrame(aFrame, aError);
         PerformNextOperation();
         break;
-#endif
+#endif // OPENTHREAD_FTD
 
     default:
         OT_ASSERT(false);
-        OT_UNREACHABLE_CODE(ExitNow()); // Added to suppress "unused label exit" warning (in TREL radio only).
-        OT_UNREACHABLE_CODE(break);
     }
 
+    ExitNow(); // Added to suppress "unused label exit" warning (in TREL radio only).
+
 exit:
     return;
 }
@@ -1548,7 +1546,6 @@ void Mac::HandleTimer(void)
 
     default:
         OT_ASSERT(false);
-        OT_UNREACHABLE_CODE(break);
     }
 }
 
@@ -1644,7 +1641,6 @@ Error Mac::ProcessReceiveSecurity(RxFrame &aFrame, const Address &aSrcAddr, Neig
 
     default:
         ExitNow();
-        OT_UNREACHABLE_CODE(break);
     }
 
     SuccessOrExit(aFrame.ProcessReceiveAesCcm(*extAddress, *macKey));
diff --git a/src/core/mac/mac.hpp b/src/core/mac/mac.hpp
index b345b8234..1276fb096 100644
--- a/src/core/mac/mac.hpp
+++ b/src/core/mac/mac.hpp
@@ -936,7 +936,7 @@ private:
 
 #if OPENTHREAD_CONFIG_MAC_FILTER_ENABLE
     Filter mFilter;
-#endif // OPENTHREAD_CONFIG_MAC_FILTER_ENABLE
+#endif
 
     KeyMaterial mMode2KeyMaterial;
 };
diff --git a/src/core/mac/sub_mac.cpp b/src/core/mac/sub_mac.cpp
index aacef704b..0b8fbe71d 100644
--- a/src/core/mac/sub_mac.cpp
+++ b/src/core/mac/sub_mac.cpp
@@ -318,7 +318,7 @@ void SubMac::HandleReceiveDone(RxFrame *aFrame, Error aError)
                      static_cast<uint32_t>(aFrame->mInfo.mRxInfo.mTimestamp) - mCslSampleTime.GetValue());
 #endif
     }
-#endif
+#endif // OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
 
 #if OPENTHREAD_CONFIG_MAC_FILTER_ENABLE
     if (!mRadioFilterEnabled)
@@ -413,7 +413,7 @@ exit:
 void SubMac::StartCsmaBackoff(void)
 {
     uint32_t backoff;
-    uint32_t backoffExponent = kMinBE + mTransmitRetries + mCsmaBackoffs;
+    uint32_t backoffExponent = kCsmaMinBe + mTransmitRetries + mCsmaBackoffs;
 
 #if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     if (mTransmitFrame.mInfo.mTxInfo.mTxDelay != 0)
@@ -446,9 +446,9 @@ void SubMac::StartCsmaBackoff(void)
 
     VerifyOrExit(ShouldHandleCsmaBackOff(), BeginTransmit());
 
-    if (backoffExponent > kMaxBE)
+    if (backoffExponent > kCsmaMaxBe)
     {
-        backoffExponent = kMaxBE;
+        backoffExponent = kCsmaMaxBe;
     }
 
     backoff = Random::NonCrypto::GetUint32InRange(0, static_cast<uint32_t>(1UL << backoffExponent));
@@ -477,8 +477,6 @@ void SubMac::BeginTransmit(void)
 {
     Error error;
 
-    OT_UNUSED_VARIABLE(error);
-
 #if !OPENTHREAD_MTD && OPENTHREAD_CONFIG_MAC_CSL_TRANSMITTER_ENABLE
     VerifyOrExit(mState == kStateCsmaBackoff || mState == kStateCslTransmit);
 #else
@@ -498,12 +496,14 @@ void SubMac::BeginTransmit(void)
     }
 
     error = Get<Radio>().Transmit(mTransmitFrame);
+
     if (error == kErrorInvalidState && mTransmitFrame.mInfo.mTxInfo.mTxDelay > 0)
     {
         // Platform `transmit_at` fails and we send the frame directly.
         mTransmitFrame.mInfo.mTxInfo.mTxDelay         = 0;
         mTransmitFrame.mInfo.mTxInfo.mTxDelayBaseTime = 0;
-        error                                         = Get<Radio>().Transmit(mTransmitFrame);
+
+        error = Get<Radio>().Transmit(mTransmitFrame);
     }
 
     SuccessOrAssert(error);
@@ -1128,7 +1128,7 @@ void SubMac::HandleCslTimer(void)
     }
 }
 
-void SubMac::GetCslWindowEdges(uint32_t &ahead, uint32_t &after)
+void SubMac::GetCslWindowEdges(uint32_t &aAhead, uint32_t &aAfter)
 {
     uint32_t semiPeriod = mCslPeriod * kUsPerTenSymbols / 2;
     uint32_t curTime    = static_cast<uint32_t>(otPlatRadioGetNow(&GetInstance()));
@@ -1140,8 +1140,8 @@ void SubMac::GetCslWindowEdges(uint32_t &ahead, uint32_t &after)
     semiWindow = elapsed * (Get<Radio>().GetCslAccuracy() + mCslParentAccuracy) / 1000000;
     semiWindow += mCslParentUncert * kUsPerUncertUnit;
 
-    ahead = (semiWindow + kCslReceiveTimeAhead > semiPeriod) ? semiPeriod : semiWindow + kCslReceiveTimeAhead;
-    after = (semiWindow + kMinCslWindow > semiPeriod) ? semiPeriod : semiWindow + kMinCslWindow;
+    aAhead = (semiWindow + kCslReceiveTimeAhead > semiPeriod) ? semiPeriod : semiWindow + kCslReceiveTimeAhead;
+    aAfter = (semiWindow + kMinCslWindow > semiPeriod) ? semiPeriod : semiWindow + kMinCslWindow;
 }
 #endif // OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
 
diff --git a/src/core/mac/sub_mac.hpp b/src/core/mac/sub_mac.hpp
index e761b8fb0..7155fa13c 100644
--- a/src/core/mac/sub_mac.hpp
+++ b/src/core/mac/sub_mac.hpp
@@ -575,11 +575,11 @@ private:
 #if OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE
     static void HandleCslTimer(Timer &aTimer);
     void        HandleCslTimer(void);
-    void        GetCslWindowEdges(uint32_t &ahead, uint32_t &after);
+    void        GetCslWindowEdges(uint32_t &aAhead, uint32_t &aAfter);
 #endif
 
-    static constexpr uint8_t  kMinBE             = 3;   // macMinBE (IEEE 802.15.4-2006).
-    static constexpr uint8_t  kMaxBE             = 5;   // macMaxBE (IEEE 802.15.4-2006).
+    static constexpr uint8_t  kCsmaMinBe         = 3;   // macMinBE (IEEE 802.15.4-2006).
+    static constexpr uint8_t  kCsmaMaxBe         = 5;   // macMaxBE (IEEE 802.15.4-2006).
     static constexpr uint32_t kUnitBackoffPeriod = 20;  // Number of symbols (IEEE 802.15.4-2006).
     static constexpr uint32_t kAckTimeout        = 16;  // Timeout for waiting on an ACK (in msec).
     static constexpr uint32_t kCcaSampleInterval = 128; // CCA sample interval, 128 usec.