I think these are threads used by JBoss for JNDI, etc.
Usually the default values work fine, but anyway, if you check attribute "QueueSize" in the jmx console (jboss.system -> ThreadPool) :
http://localhost:8080/jmx-console/HtmlAdaptor?action=inspectMBean&name=jboss.system%3Aservice%3DThreadPool
and see large value, you might want to increase set the pool size from 10 to a larger value.