Blocked where? Ask yourself is there really any information in your question
that makes it answerable?
These threads are part of thread pool. They're intended to block until
work is available (or they've been idle for too long and are destroyed).
I am also getting the same behavior in JProfiler. I am using JBoss 4.2.2 GA. I am having the snapshot of the JProfiler, according to the JProfiler "JMS SessionPool Worker" thread blocked since 117 seconds and still in blocked state. Monitor class it is showing is "org.jboss.mq.server.ReceiversImpl"