The opposite is 直接 (zhíjiē) = direct/directly. Both are very common in daily Chinese. 间接原因 = indirect cause. 直接原因 = direct cause.
usage
Note the pronunciation: 间 is read jiàn (4th tone) here, not jiān (1st tone). When 间 means 'gap/interval/between,' it's jiàn. When it means 'room/space,' it's jiān.
