Switch to Safe Mode and see whether the CPU usage the same, if not, there are something running at the background you need to find out. If the same, mean normal.
I had the same experience, CPU runs more than 50% & RAM more than 70% even checked task manager without any program running. It could be caused by virus, torjan horse but not detected by my NOD32 anti-virus program. Finally I have to clean up and reload my recovery disk and CPU reduce to 4% & RAM usage to 20% when just using internet browser. Now it looks normal. Please try my suggestion if you have done everything.