ORA-00054: resource busy and acquire with NOWAIT specified

Step 1: Identify the session which is locking the object
select a.sid, a.serial#
from v$session a, v$locked_object b, dba_objects c
where b.object_id = c.object_id
and a.sid = b.session_id
and OBJECT_NAME='EMP';

Step 2: kill that session using
alter system kill session 'sid,serial#';