Users who have an optical laser mouse (most common mouse for desktop computers) are likely experiencing erratic behavior because the mouse is not clean or is dirty. If you've cleaned the mouse and continue to encounter issues and this mouse has worked in the past fine unfortunately your mouse is likely defective. One additional test that can be done to help determine if this is the case or not is to connect the mouse to another computer. Otherwise we suggest replacing the mouse.
Additionally if you are using a wireless mouse, there can sometimes be interference with the USB receiver plugged into your computer. Try moving the receiver to another USB slot, or if you have an extender available use that to put the receiver further away from the computer.