My airport stays connected but no internet--what gives?

The problem I am expericing with my airport is that the airport card in my mac mini stays connected to my airport express 802.11n but I cannot use the internet at all. If I turn off my airport card and turn it back on again, then it connects to the airport express and I can use the internet for awhile until this happens again. I do not believe it's my mac mini's wireless card because I have the same experience with my iPhone 4. So I'm guessing it's the airport express. So I plugged my mini to ethernet and of course I can keep a good connection without problems. So that also eliminates the problem of an unstable internet connection. So I'm not sure if my airport express is just dying or what exactly is the problem.

Any suggestions and thanks in advance!