Most likely your query is waiting to get access to the record. You probably have modified that row in "oracle development tool" and have not committed or rolled back that transaction.
Just commit/rollback in your tool or close open session. You can check for open transactions in v$transaction view.
More on automatic locks in Oracle: http://docs.oracle.com/cd/E11882_01/server.112/e41084/ap_locks001.htm