Three people of interest also in custody, Chicago Police Department spokesman Anthony Guglielmi announced on Twitter Friday.
Officers seized the assault weapons during a traffic stop, and were "in the right place, at the right time," Officer Michelle Tannehill said at a press conference Friday.
Police believe that the offenders, who are in custody, "had ill intentions to carry out violent acts here in Chicago," Tannehill said.
The offenders haven't yet been identified. Charges are being determined, and police said they have no other information at this time.