Another device using my IP address-who?

I suspect it may have something to do with my iPad, as it's happened only since I purchased one-a wifi version. When I restart, I keep getting a message that "Another device on the network is using your computer's IP address. The thing is, it's not the IP address shown in SysPrefs/Network, nor is it the one on my wife's iMac or my MacBook Pro. Is this something to be concerned about?