diff --git a/src/posix/platform/radio_spinel.cpp b/src/posix/platform/radio_spinel.cpp
index 8cd57df8a..33f93f53a 100644
--- a/src/posix/platform/radio_spinel.cpp
+++ b/src/posix/platform/radio_spinel.cpp
@@ -54,55 +54,8 @@
 #include <openthread/platform/diag.h>
 #include <openthread/platform/radio.h>
 
-enum
-{
-    IEEE802154_MIN_LENGTH = 5,
-    IEEE802154_MAX_LENGTH = 127,
-    IEEE802154_ACK_LENGTH = 5,
-
-    IEEE802154_BROADCAST = 0xffff,
-
-    IEEE802154_FRAME_TYPE_ACK    = 2 << 0,
-    IEEE802154_FRAME_TYPE_MACCMD = 3 << 0,
-    IEEE802154_FRAME_TYPE_MASK   = 7 << 0,
-
-    IEEE802154_SECURITY_ENABLED  = 1 << 3,
-    IEEE802154_FRAME_PENDING     = 1 << 4,
-    IEEE802154_ACK_REQUEST       = 1 << 5,
-    IEEE802154_PANID_COMPRESSION = 1 << 6,
-
-    IEEE802154_DST_ADDR_NONE  = 0 << 2,
-    IEEE802154_DST_ADDR_SHORT = 2 << 2,
-    IEEE802154_DST_ADDR_EXT   = 3 << 2,
-    IEEE802154_DST_ADDR_MASK  = 3 << 2,
-
-    IEEE802154_SRC_ADDR_NONE  = 0 << 6,
-    IEEE802154_SRC_ADDR_SHORT = 2 << 6,
-    IEEE802154_SRC_ADDR_EXT   = 3 << 6,
-    IEEE802154_SRC_ADDR_MASK  = 3 << 6,
-
-    IEEE802154_DSN_OFFSET     = 2,
-    IEEE802154_DSTPAN_OFFSET  = 3,
-    IEEE802154_DSTADDR_OFFSET = 5,
-
-    IEEE802154_SEC_LEVEL_MASK = 7 << 0,
-
-    IEEE802154_KEY_ID_MODE_0    = 0 << 3,
-    IEEE802154_KEY_ID_MODE_1    = 1 << 3,
-    IEEE802154_KEY_ID_MODE_2    = 2 << 3,
-    IEEE802154_KEY_ID_MODE_3    = 3 << 3,
-    IEEE802154_KEY_ID_MODE_MASK = 3 << 3,
-
-    IEEE802154_MACCMD_DATA_REQ = 4,
-};
-
 static ot::PosixApp::RadioSpinel sRadioSpinel;
 
-static inline bool isAckRequested(const uint8_t *frame)
-{
-    return (frame[0] & IEEE802154_ACK_REQUEST) != 0;
-}
-
 namespace ot {
 namespace PosixApp {
 
@@ -206,7 +159,6 @@ RadioSpinel::RadioSpinel(void)
     , mWaitingKey(SPINEL_PROP_LAST_STATUS)
     , mRxSensitivity(0)
     , mState(kStateDisabled)
-    , mIsAckRequested(false)
     , mIsPromiscuous(false)
     , mIsReady(false)
     , mSupportsLogStream(false)
@@ -725,7 +677,8 @@ void RadioSpinel::Process(const fd_set &aReadFdSet, const fd_set &aWriteFdSet)
         else
 #endif
         {
-            otPlatRadioTxDone(mInstance, mTransmitFrame, (mIsAckRequested ? &mAckRadioFrame : NULL), mTxError);
+            otPlatRadioTxDone(mInstance, mTransmitFrame, (mAckRadioFrame.mLength != 0) ? &mAckRadioFrame : NULL,
+                              mTxError);
         }
     }
 
@@ -1043,8 +996,6 @@ void RadioSpinel::RadioTransmit(void)
     otPlatRadioTxStarted(mInstance, mTransmitFrame);
     assert(mState == kStateTransmitPending);
 
-    mIsAckRequested = isAckRequested(mTransmitFrame->mPsdu) && !mIsPromiscuous;
-
     error = Request(true, SPINEL_CMD_PROP_VALUE_SET, SPINEL_PROP_STREAM_RAW,
                     SPINEL_DATATYPE_DATA_WLEN_S SPINEL_DATATYPE_UINT8_S SPINEL_DATATYPE_INT8_S, mTransmitFrame->mPsdu,
                     mTransmitFrame->mLength, mTransmitFrame->mChannel, mTransmitFrame->mInfo.mRxInfo.mRssi);
@@ -1189,11 +1140,14 @@ void RadioSpinel::HandleTransmitDone(uint32_t          aCommand,
         aBuffer += unpacked;
         aLength -= static_cast<spinel_size_t>(unpacked);
 
-        if (mIsAckRequested)
+        if (aLength > 0)
         {
-            VerifyOrExit(aLength > 0, error = OT_ERROR_FAILED);
             SuccessOrExit(error = ParseRadioFrame(mAckRadioFrame, aBuffer, aLength));
         }
+        else
+        {
+            mAckRadioFrame.mLength = 0;
+        }
     }
     else
     {
@@ -1567,7 +1521,8 @@ void ot::PosixApp::RadioSpinel::Process(const Event &aEvent)
         else
 #endif
         {
-            otPlatRadioTxDone(mInstance, mTransmitFrame, (mIsAckRequested ? &mAckRadioFrame : NULL), mTxError);
+            otPlatRadioTxDone(mInstance, mTransmitFrame, (mAckRadioFrame.mLength != 0) ? &mAckRadioFrame : NULL,
+                              mTxError);
         }
     }
 
diff --git a/src/posix/platform/radio_spinel.hpp b/src/posix/platform/radio_spinel.hpp
index c7f7321ff..ce872ad5c 100644
--- a/src/posix/platform/radio_spinel.hpp
+++ b/src/posix/platform/radio_spinel.hpp
@@ -609,7 +609,6 @@ private:
     char         mVersion[kVersionStringSize];
 
     State mState;
-    bool  mIsAckRequested : 1;    ///< Ack requested.
     bool  mIsPromiscuous : 1;     ///< Promiscuous mode.
     bool  mIsReady : 1;           ///< NCP ready.
     bool  mSupportsLogStream : 1; ///< RCP supports `LOG_STREAM` property with OpenThread log meta-data format.