You should call your ISP to discuss this. The steps necessary to correct the problem. There IS a problem, even if it's not affecting you yet, it likely will at some point in the future.
What you need to do depends on your circumstances, which they should know better. The most likely cause is your router is handing out 10.0 addresses and that's the address YOU have been handed out also. There's also the possibility they aren't correctly isolating traffic, or that your airport is or needs to be on pass-through, or that your airport has detected another router on their network with the same IP address as yours. (not good)
Call them and sort it out. Don't ignore the error. If they tell you to just ignore it or try to walk you through the steps to tell the airport to stop notifying you of the problem, dig deeper if you can. (talk with a higher level tech)
The last time I ran into something like this, the clowns had misconfigured their new DSLAM firewall and EVERYONE had access to EVERYONE ELSE'S network. I opened network browser and saw shared computers and printers all over town, and could connect to them, print to their printers, etc. Imagine the worm/virus traffic on a misconfigured network like that today!
