diff --git a/src/ncp/ncp_base_radio.cpp b/src/ncp/ncp_base_radio.cpp
index 6fb67b8d0..9eb87fcb1 100644
--- a/src/ncp/ncp_base_radio.cpp
+++ b/src/ncp/ncp_base_radio.cpp
@@ -195,10 +195,17 @@ void NcpBase::LinkRawTransmitDone(uint8_t aIid, otRadioFrame *aFrame, otRadioFra
             uint8_t  keyIndex;
             uint32_t frameCounter;
 
-            // Transmit frame auxiliary key index and frame counter
-            SuccessOrExit(static_cast<Mac::TxFrame *>(aFrame)->GetKeyIndex(keyIndex));
             SuccessOrExit(static_cast<Mac::TxFrame *>(aFrame)->GetFrameCounter(frameCounter));
 
+            // If the frame uses Key ID Mode 0, there is no Key Index field in
+            // the Security Header, so `GetKeyIndex()` may return an error.
+            // We default `keyIndex` to 0 in this case.
+
+            if (static_cast<Mac::TxFrame *>(aFrame)->GetKeyIndex(keyIndex) != OT_ERROR_NONE)
+            {
+                keyIndex = 0;
+            }
+
             SuccessOrExit(mEncoder.WriteUint8(keyIndex));
             SuccessOrExit(mEncoder.WriteUint32(frameCounter));
         }