Suppose: You killed the session of a scheduler job step, in spite of that this step and with it entire job and seemes to be keep on running (e.g. in OEM).

Solution: Find out the obj# of your job

DELETE FROM scheduler$_step_state WHERE job_oid = <your job id>;
UPDATE scheduler$_job SET job_status = job_status - bitand(job_status, 258) WHERE obj# = <your job id>;
COMMIT;