Hi friend - is your mouse wireless/radio as opposed to wireless/infra red? If radio it is possible that someone living nearby also has a radio mouse on the same channel as yours. If this is the case, change your channel, there is a little switch on mouse to enable this. If it is NOT radio then it is possibly virus related or - after all that, if your mouse has a ball, then you probably need to remove ball and clean rollers inside mouse.
Phew - did I say all that? Hope something there helps anyway.