Illinois State Police were notified of a pursuit out of Wisconsin involving the bus, police said.
Passengers were removed from a Greyhound bus traveling eastbound on I-94 near north suburban Wadsworth after reports of a disorderly and possibly armed passenger, who is now in custody. A man with a gun was reportedly on the bus, the Lake County sheriff's office said.
The bus eventually stopped on I-94 at Rt. 173.
Officials say all 50 passengers were evacuated from the bus, and a suspect is in custody.
Traffic was closed in both directiions on the interstate while police continue to investigate, the Daily Herald reported.
Authorities said no injuries were reported.
Greyhound released a statement saying police from several counties responded to the scene. Motorists are advised to avoid the area.