Try using nohup, or better yet set up JBoss AS to run as a service and start it as a service.
How do you get JBoss running as a service.
In general, look in the jboss_home/bin directory at the jboss-init-*.sh files. Use one of them, modified for your environment, as the file that goes into /etc/init.d. Then the exact steps for making the app server start when your machine boots (if you want to do that) differe based on the OS. But googling how to do that for your OS should yield many instructions.