The air parcel was booked at St Thomas Mount Head Post office near the airport. It was later moved to the cargo complex for loading it into a SpiceJet airline.
During mandatory screening process, it was found that the parcel had a revolver concealed in it. The weapon has been seized.
A probe is on to establish leads like the authenticity of consignor and consignee, the source and intended use of weapon and other things, police sources said.