Even if no application is deployed on JBOSS 4.2.2, it is taking more than 100% CPU on my linux machine.
That does sound a bit odd indeed. However JBoss has got quite a lot out-of-the-box services enabled that could take CPU. If you do a stack trace (send java the -QUIT signal) you can see what threads are running. Sometimes the deployment scanner thread can run wild (the thread that auto deploys resourced placed in the deploy/ directory).
As a last resource check if JBoss is going garbage collection, simply add the verbose gc JVM arguments to your run.conf file.