The pair faced life behind bars when they were indicted last summer on charges including arson, conspiracy and use of explosives.
As anti-cop protesters faced off with police outside the 88 Precinct stationhouse on May 29, Rahman allegedly tossed a Molotov cocktail at an empty NYPD van nearby.
Mattis acted as the wheelman during the firebombing and drove off after the van ignited, but the two were arrested a short while later, prosecutors allege.
Prosecutors said in a detention memo at the time that they were trying to pass out Molotov cocktails to protesters at the demonstration.