I would not be worried about a NetBIOS name query coming from my router.
I've seen many routers that when you go into their MAC filtering options (or any option that works using MAC addresses) will also show the NetBIOS name that has been set on that PC. This makes it easier to work out what machines are yours on the network and restrict them as necessary.
If you are still uncertain then what I would do is go to grc.com and use their Shields Up! tools to scan your ports and make sure that port 137 is closed on the internet side of your router. This way you can be sure that the name probe packets are coming from your router itself and not the internet at large.