Hey Azmir
As everyone has explained, the lens on the bottom of the magic mouse sometimes becomes dirty, smudged, and even some cases can develop scratching.
Most of the time the problem is the mouse not recognizing the movement of your hand. This is because the laser can't detect a surface. As everyone has said, check the clarity of the lens first. If you have done so and the problem still persist, check the bluetooth connection. Make sure there are no other connected mice, usb mice, or other unknown bluetooth devices in the "Bluetooth" pane.
Assuming this is the original Apple Magic Mouse check the terminal connections for the batteries too. If there isn't enough power circulating the mouse due to corrosion of the terminals, some features or normal behavior may diminish.