The man has been identified as Rahul. He was arrested while on way to meet his gang leader Neeraj Bawana at Rohini court, police said.
A country made 9 mm automatic pistol and live cartridges were recovered from him, they said.
During interrogation, Rahul told police that he is the brother of an aide of Bawana, a gangster arrested for extortions last year, and is presently lodged at Tihar Jail.
Last week, the gang on instructions from their jailed leader hatched a plan to free a murder accused, Vikas Lagarpuria, from police custody while he was being taken to court. However, they didn't succeed as the police foiled the escape bid.