What kind of mouse? USB or ps/2? Have you tried the obvious: Restarting your computer? Someone could be connected to your pc with remote connection so, try unplugging your internet cable.
restarted the computer but it kept doing the same thing
unpluged the ethernet cable but it kept on going
edit: just got on my other copmuter while the virus scan is running, this has been going on for 3 days and i though it was just a bad mouse but I just picked up a new one and it did the same thing. It seems to go away when I restart the computer but comes back when it's on for a few minutes
I've never heard of this problem before but it sounds like it could be a virus or maybe your port is bad. I would try using your new mouse on another computer to make sure it works. Then if it does work, try running a virus scan on your computer. If the problem still persists try backing up your files and doing a destructive restore on your computer. If all that doesn't work you have a inner hardware problem. Try contacting the manufacturer for troubleshooting steps to find out where.