diff --git a/src/ncp/ncp_base.cpp b/src/ncp/ncp_base.cpp
index 9803ba95a..f4baf6265 100644
--- a/src/ncp/ncp_base.cpp
+++ b/src/ncp/ncp_base.cpp
@@ -604,7 +604,7 @@ void NcpBase::Log(otLogLevel aLogLevel, otLogRegion aLogRegion, const char *aLog
     otError error  = OT_ERROR_NONE;
     uint8_t header = SPINEL_HEADER_FLAG | SPINEL_HEADER_IID_0;
 
-    VerifyOrExit(!mDisableStreamWrite);
+    VerifyOrExit(!mDisableStreamWrite, error = OT_ERROR_INVALID_STATE);
     VerifyOrExit(!mChangedPropsSet.IsPropertyFiltered(SPINEL_PROP_STREAM_LOG));
 
     // If there is a pending queued response we do not allow any new log
@@ -1172,6 +1172,8 @@ otError NcpBase::CommandHandler_RESET(uint8_t aHeader)
         mUpdateChangedPropsTask.Post();
     }
 
+    sNcpInstance = NULL;
+
     return error;
 }