It could be a broken mouse or a very slow processor and if you perocessor is fast enough then there is a software or spyware running on your computer which is loading you cpu to it's maximum.
There are more posibilities but these are the most common ones.
Recently i have noticed that my mouse is jumpy. When I move to a location or move very slowly the mouse seems to jump a bit further or move up or down. The whole system is only about 6 months old. I have cleaned the mouse and tried to remove the mouse pad. I have tinkered with the settings in the properties without sucess. It is just a standard wheel mouse from MS.