Nine firearms, two magazines, 47 cartridges and five kg of bomb making materials were found in a sack from the bus.
The police, on a tip off, intercepted the bus when it entered Canning, searched the vehicle and found the sack.
Two persons - Shamim Khan and Sheikh Salim - were arrested, police said adding they were also looking for a woman involved in the incident.
The consignments came from Munger in Bihar.
The bus was plying between Sonakhi in Basanti area to Jamtala in Kultali of the district.