Around 5:30 a.m. the Chicago Transit Authority announced minor delays for the Red, Brown and Purple lines in Lakeview.
The CTA said trains were standing due to a "an unauthorized person on the tracks" near the Belmont Station.
The person did not have contact with the train or the third rail, according to a CTA spokesperson.
By 6 a.m. all trains were running with minor delays.
The person was taken to the hospital while in custody, according to CTA.
The man was alert and speaking to police.
This happened as a "mass arrest" was ordered blocks away at Clark Street near Halsted Street.
It is unknown if the two events are connected.
This is a developing story.
READ ALSO | Mass arrest ordered in Lakeview near Chicago Pride Parade location, police say