If you got a virus checker, make sure it is up to date, then run it. To an indepth check. Doubt that it is a virus, but worth the effort anyway.

Mice don't last forever. Better to replace than investigate. Go buy a Microsoft Wireless 3000 USB Optical Notebook Mouse for about $20. Plug it in to your USB port and go. Takes one AA battery (included). Still has the wheel but no stupid little rubber ball to get all gunked up. I've been using one for over a year. Replaced battery once, when cursor became erratic. Plus no wire, so you don't have to stay 3 feet away from your computer to use it.

If you don't have a USB port (you didn't say how old the computer is) just go get a new mouse of the wired variety. Odds are the problem is in the mouse.