Police said someone inside a van pointed a pistol at Acevedo, but the vehicle sped away when the representative announced his office.
A police spokesman wasn't aware whether Acevedo -- a state representative since 1997 and a Chicago police officer since 1995 -- identified himself as an elected official or as a police officer.
No arrests have been made and police didn’t release a description of the van or the gunman inside.
Investigators weren't clear on a motive for the incident.
Acevedo, 47, won re-election in 2nd District on Chicago's West and Southwest Side in last November's general election after running unopposed. He wasn't immediately available for comment this afternoon.