Is it a USB or PS2 mouse? What OS?
Anyway, did you check in Device Manager to see if it says anything (other than device is working properly)? Assuming you did and it says device is okay, try booting into safe mode. If the mouse does the same thing, you may have a bad driver. Try downloading the latest driver.
Also, did you recently change your mouse? If you did, you might still have the driver for the previous mouse installed on your machine which is conflicting with the new mouse's driver.
Lastly, you might have a mobo problem - check to see if there's a hardware conflict. Do you have the latest BIOS updates?