A security guard spotted the monkey near ticket gates in Shibuya Station, said Norihiru Masui, a spokesman for train operator Tokyu Corp.
The monkey climbed to a perch high atop a departure board, and around 30 policemen surrounded the area and attempted to snare it with a variety of nets, as commuters crowded around and snapped pictures with their cell phones.
The standoff ended when the monkey climbed down and dashed out of the station, with several policeman and local TV crews in tow. News reports said the monkey was last seen heading in the direction of nearby Yoyogi Park.
The animal appeared to be a Japanese monkey, which are native to the country, and was about 27 inches (70 centimeters) long from head to the tip of the tail. No one was injured and no trains were delayed in the incident.
Japanese media have reported several monkey sightings in Tokyo recently, but it was unclear if they involved the same animal.
Monkeys have long made appearances in rural parts of Japan, where they have been known to damage crops, swipe food from grocery stalls and even bite humans. In recent years, growth in the monkey population has meant more frequent forays out of the forests and into farms and towns.