CBI sources said Mittal was questioned in connection with details of promotions and postings of Board members yesterday evening.
Underlining that Mittal was not questioned as accused,, CBI sources said he was questioned for three hours starting 5 PM.
The case relates to alleged bribe payment to Singla by Board member Mahesh Kumar for getting posting of choice.
Bansal had to resign as Union Railway Minister early this month after his nephew and a few other persons were arrested by CBI in a case involving alleged payment of bribe for fixing a top level Railway Board position.