First and foremost, WELCOME to Sandy's CompuKISS site where youwill find lots of nice folks and a lot of very helpful information that Sandy has along the left side of your browser window....
One thing that helps on forums to give those who try to give answers to problems is a lot of information from the poster about their system, perhaps programs being used, those bits and pieces of info that can help shed light on a problem and possible solution......
here are a few that will help....... What kind of mouse are you using? Is it wired or wireless, does it have a roller ball on the bottom, or does it shine a red or blue light thru the bottom and onto the mouse pad or surface? Is it battery operated for power, or does it sit in a charger/holder to keep the bateries charged - if it is a battery operated mouse.
As you can see, solutions could run from a driver problem, a dirty mouse ball, a weak battey, a glossy surface reflecting the motion light..... and others......
Gee, sorry for all the questions... that's a heck of a way to welcome someone...

.... but info is so helpful to finding a solution to a problem...

While we're waiting, here is some Mac mouse info for you.......
http://www.myfirstmac.com/index.php/mac/articles/what-are-my-choices-in-using-a-mouse-with-my-new-macAgain, though, welcome to Sandy's site.........