Transit Police arrested a woman at the Brookline Hills MBTA station Tuesday night ­after she allegedly threatened several men with a knife while riding on the Green Line.

Police said Madina Clayton, 52, of Boston, pulled out a small folding knife as she sat on the Riverside Line train. While sitting across from a male passenger, Transit Police said, Clayton repeatedly opened and closed the knife while staring at the man.

When he got up to move to another part of the train, she stood up, pointed the knife at him, and shouted an obscenity, police said.

The woman then engaged another male passenger, accord­ing to police. When he, too, tried to change seats, she followed him with the open knife, Transit Police said.

Witnesses told police the woman swung the knife “haphazardly” at a third male passenger as he was exiting the train.

Transit and Brookline police responded at 9:45 p.m. and ­arrested Clayton on a charge of assault with a dangerous ­weapon.

Officers also discovered there was an arrest warrant ­issued for Clayton by Boston Municipal Court on a charge of ­assault and battery with a dangerous weapon, Transit Police said.

At Transit Police headquarters, police said, officers found she was in possession of marijuana, for which she was cited.

Clayton was not arraigned in Brookline District Court Wednesday, but was instead taken to Taunton State Hospital for a competency evaluation, at the request of her legal counsel. She will be arraigned Dec. 20.