To Get Jobs Under A Particular Category

Hi,
When I m trying to get job list by passing arguments ,I m unable to list the jobs which are under particular category.

$query_args = array(
'post_type'              => 'job_listing',
'category' => $cat_id,//$cat_id = 31 
'post_status'      => 'publish',
 );
 $results = new WP_Query( $query_args );

In results, getting all the jobs rather than the jobs in particular category.

Can you pls,help me out.

Thanks In Advance.