The 605 Freeway in the Baldwin Park and Irwindale areas was reopened after lanes were shut down in both directions Wednesday night, the California Highway Patrol said.
The CHP cited "police activity," and initial reports from the scene were that a person possibly armed with a weapon was threatening to jump onto the busy artery that connects the San Gabriel Valley with southeast Los Angeles County.
The closure lasted about 45 minutes before a suspect was taken into custody by officers.
Earlier, northbound traffic was being diverted off the freeway at Ramona Boulevard, and southbound traffic was being diverted at Lower Azusa Road.
No other details were immediately available.