The depositors gathered outside the RBI around 11.45 am and held protests by showing placards and chanting slogans against PMC Bank and the RBI, a police official said.
Police were deployed to avert any untoward incident, he said, adding that nobody has so far been detained or taken into custody.
After an alleged Rs 4,355 crore scam came to light at the PMC Bank, the RBI initially capped withdrawals at Rs 1,000 in view of liquidity crisis, and later hiked it to Rs 40,000 in three moves.
The depositors have been protesting to get their money back.
Singh was a director of the bank and is the son of senior state BJP leader Sardar Tara Singh, a former legislator from Mulund.
According to Mumbai Police spokesperson and Deputy Commissioner of Police Pranaya Ashok, Rajneet Singh was brought for questioning in connection with the Rs 4,355 crore fraud allegedly perpetrated by PMC Bank directors and directors of the HDIL group.
Since Rajneet was a director at the bank for around 13 years besides being a member of the bank's Recovery Committee, he was interrogated on the loans extended to the HDIL group companies, their long-pending dues and the efforts made to recover the same.
However, he provided evasive and unsatisfactory explanations after which his involvement in the offences was revealed and confirmed by the investigators.
Accordingly, he was arrested late in the evening and will be produced before a holiday magistrate on Sunday for securing police remand for further investigation, said the DCP.
So far, over half a dozen persons, including PMC Bank's senior past and present executives, and the top brass of the HDIL group have been arrested since the scam erupted in late September.