iMac And Mouse pointer randomly changing size

I have a late 2012 21.5” iMac Model Number MD093LL/9. Over the last few weeks I have noticed the mouse pointer on screen randomly increasing briefly in size from the normal to about 2cm or so before returning to normal. This occurs at different positions on the screen with no apparent pattern although the frequency appears to be increasing - more than once in every session.

Is this a sign of problems now or ones to come?

Is there a solution?

Thanks for any information