Oh, Ya, I know before killing one should check what locked it and thanks, I had done that. Even without doing that I knew what did it. In my original post I did mention that this is my test database and I was testing something !!!!

Thanks to all for their suggestions. It did release locks on that table after sometime.
Few more things as rohitsn suggested I had tried to do:
SQL>truncate table temp NOWAIT;
But kept getting same error message.

Also, this query returned 0 records and still the table was locked !!
select object_name,os_user_name from v$locked_object a,dba_objects b
where a.object_id = b.object_id ;

One thing which I don't understand is when I did select * from v$session all the sessions accessing this db showed that they were killed. I was logged in as System/manager.
Also I am the only user on this db. What kept it locked even when all sessions were killed ???

Thanks again