What was the application that held onto that port? Does it hold onto the same port when you launch it after a reboot? If yes, this is definitely something that you should be worried about but my guess is that the port will be different after a reboot. (If the port is different then it is probably just a normal use of ephemeral ports.) Port Explorer, as Jooske suggested, is the surest way to gauge whether this is something that needs to be further scrutinized.
Thanks for the replies, I was using TDS3 netstat tool, I have not seen it again on the last 3 occasions that I have started up.