Police said a man and woman in their 20s were held up near West Berteau and North Kedvale avenues, just after 7 a.m. in the Old Irving Park neighborhood.
The victims complied, but the 19-year-old suspect still battered them, police said.
Both victims were taken to the hospital with non-life-threatening injuries.
Police said they recovered a firearm and the 19-year-old is in custody. Charges are pending.
INTERACTIVE SAFETY TRACKER Track crime and safety in your neighborhood