diff --git a/tools/harness-thci/OpenThread.py b/tools/harness-thci/OpenThread.py
index 330a556c4..3b1a99415 100644
--- a/tools/harness-thci/OpenThread.py
+++ b/tools/harness-thci/OpenThread.py
@@ -2870,7 +2870,7 @@ class OpenThreadTHCI(object):
                 self.bbrSeqNum = 128
             else:
                 self.bbrSeqNum = (self.bbrSeqNum + 1) % 256
-        else:
+        elif SeqNum is not None:
             self.bbrSeqNum = SeqNum
 
         return self.__configBbrDataset(SeqNum=self.bbrSeqNum, MlrTimeout=MlrTimeout, ReRegDelay=ReRegDelay)