wireless connection working intermittently

Hi,

I have a router-AP(r1) and a computer connected to r1 via wireless connection.

r1-192.168.1.3
computer 192.168.1.20,DNS 192.168.1.1, gateway 192.168.1.3

My problem is the computer wireless connection works for about 3-5 minutes. Then
goes down (can't connect to r1) for about 1-2 minutes. Then starts working again.

Any ideas what can cause this?

Any ideas appreciated.

Guy