CPU = central processing unit, which is the bit of your computer which does all the work.
High CPU use can come about through a virus or malware hogging all of your computer's resources but it can also occur because a program (or part of a program) isn't functioning properly, or because two conflicting programs on your computer are trying to use the same resources simultaneously.
When you see the message again, press Ctrl-Alt-Delete to enter the Task Manager. Click on the Processes tab and look down the CPU column. (That tells you the percentage of available processing power which each program component is using). Normally the only figure above 10% should be against 'System Idle Process'. If anything else is particularly high, that's probably the cause of your problem. (Post again, telling us what process has a high figure, for advice as to what to do).
Also check whether any malware has found its way onto your computer by downloading, installing and running the free version of Malwarebyte's Anti-Malware:
http://www.malwarebyt...ts/malwarebytes_free/
Chris