The "normal range" depends on what processes are running and what applications are open. This changes from moment to moment, depending on what is installed and running.
Example: If an AV scan...or a malware scan...or probably any other type of scan by software installed...is running, the CPU usage will increase. How much is a variable.
If you can post a picture of Task Manager when you think that it's too high, that would be useful. There are two tabs that should be posted, Applications and Processes. Before posting Processes, click on the percentage/use column so that the heavy users will be at the top, then take the picture.
FWIW: Being connected to the Internet...is not the same as having one or more Windows open which are on the Web. Every window opens requires a little more CPU power, even though there is only one Internet connection. The connection is important...but the number of connections to the Internet via the cable connection...is more important.
Edited by hamluis, 10 April 2008 - 01:45 PM.