Laptop Wifi Occasionally Drops?

When I'm next to the room where the router is, the WiFi connection sometimes just drops. I'd say that I can surf something like 2-3 minutes and then all of sudden the WiFi connection drops, and the WiFi tray icon says that I have a limited connection. Though the signal quality is 4, and sometimes even 5 (which is maximum). And then it takes like 15-20 seconds to get everything back to normal again. But then again.. when I was in the same room as my router, actually on the same desk as the router, I didn't have any problems with WiFi dropping - I think I'll test later tonight again, if there's really a difference if I sit basically next to the router and then when I go to the other room, the connection starts dropping every once in a while (and remember, I still have an excellent signal quality). And I'll add just in case that I haven't had any problems with wired connection. And in our household we've got one laptop more, and this one hasn't had any problems with WiFi dropping. So.. it must be something with my laptop.. I guess.

- WiFi network card: Atheros Communications AR9485 Wireless Network Adapter

According to device manager:
Driver date: 3.10.2011
Driver version: 9.2.0.458

- Second network card (for wired connection, I guess): Attansic (Now owned by Atheros) AR8161 Gigabit Ethernet

According to device manager:
Driver date: 16.01.2012
Driver version: 2.0.12.13

- OS: Windows 7 64 bit

- Router: SpeedTouch 780WL - Software release: 7.4.4.7

- Anti-virus: McAfee Internet Security | Can't tell you the exact version, because it has different versions for different things. For example SecurityCenter has v11.0 and VirusScan has v15.0. Just to add that I've heard that some people have had problems with WiFi, and it has been anti-virus' fault. Well.. I'm not planning to keep McAfee, I'll get rid of it soon. But I think it might help if I mention the anti-virus program too.