I've had an issue with the first Lenovo I had bought, the A600. Right out of the box, within the first 24 hours of use, the mouse would freeze and the pointer locked up. After having replacemets sent of both the mouse and keyboard as both were giving me trouble from the get-go, I got the B500 instead.
All seemed fine and dandy until a few weeks ago, the same thing started to happen. It happened intermittently, and then wouldn't happen again for a few weeks (I've only had this computer for 2 months at the time of this writing) It started to happen more so a few weeks ago, then stopped, did it a few times here and there. As of yesterday, it was bad, this morning it was worse. It was doing it excessively. In a 10 minute time span it did it each and every minute. As soon as I was able to get it back up and moving it would lock / freeze again.
Finally, I went to change the batteries. I had used the batteries that came with the unit originally and changed them for Duracell batteries. It seemed to do the trick, at least it has at this time. I would not have thought it could be the battery in just the small amount of time we've had this computer and the little bit of usage it's been given. It originally seemed to happen only when I was pulling down the blue scroll bar on the side of the screen, then it started happening on other areas of the screen.
Perhaps the original batteries were weak - as such, it seems prudent to check / replace the batteries if operation is erratic before replacing hardware. See other articles on updates to improve pairing on B500 bluetooth keyboard & Mouse.