You could try disconnecting the mouse and reconnecting it (Bluetooth or USB?) or you could use the trackpad built into the MBA or you could use the power button and press it and select Restart from the following dialog or you could hold down the power button to shut down the MBA and press it again to start it up.
Btw, what MBA and Mac OS X version and what mouse are you using?
Maybe you need to clean your mouse between the button(s) and the body?