High CPU Usage Warnings

I’ve been getting Norton 360 warning messages telling me that I am having high CPU usage by various applications such as Internet Explorer, Office Word and Office Excel. Norton even gives me messages that say an application has high CPU usage when I am not using that application, e.g. Office Word or Office Excel. Apparently something is going on which causes Norton to give me the High CPU Usage messages but I don’t know what it could be. Can someone help me with this problem?