Mr Kumar was produced before Special CBI Judge Swarana Kanta Sharma who remanded him to custody till May 9 after the investigating agency said he is the main accused in the case and his custodial interrogation was required to unearth the entire conspiracy.
The CBI had sought five-day police custody of Mr Kumar, saying he is the one for whom the entire arrangement was being made.
Besides Mr Kumar, CBI has arrested Mr Bansal's nephew Vijay Singla and six others for their alleged roles in the bribery case, in which a deal of Rs 10 crore was finalised between them for fixing a top-level position for Mr Kumar in the Railway Board.
"The invesigation is at an initial stage and Mahesh Kumar is evasive in his answers and is not cooperating. He is not giving us proper replies to the questions being asked," CBI prosecutor Akshay Gautam told the court.
CBI also said they have to arrest two more accused in the case.
Mr Kumar was arrested from Mumbai and was brought here on transit remand.
Mr Kumar, who was GM (West) Railways, had been recently promoted as Member (Staff) in Railway Board and was allegedly trying to get himself posted as Member (Electrical).