Those are MAC (Media Access Control) addresses that router forbids to access wireless network you have. Every network card has MAC address associated with to be uniquely identified, in your case (if you do not configured it yourself) it blocks those addresses probably because they have tried to access or use your network. That's the way to prevent users from using your wireless network, if WEP (Wired Equivalent Privacy) encryption is used, then for knowledgeable people is very easy to obtain your password for wireless network access, and actually use it without your knowledge. It is advisable to use WPA-2PSK encryption instead.
You can check what encryption you are using, and ask us more... Thanks