Yeah, not normal... I know there have been some reports that plugging the phone in to a computer via USB can cause it to cycle the CPU rather high. If you're doing that, stop it!

I also know there have been a couple apps that when installed can cause other apps or system components to run heavy CPU. Have you been seeing short battery life as well? If so, that may be whats getting you.

Check out the app manager for "Load Applet", which shows the CPU use in the top bar. If that shows activity, top or Conky can show you what the culprit process is. Based on that info we may be able to better diagnose whats going on. Good luck!