Police arrested 39-year-old Stuart Cato and charged him with Forcible Touching, Harassment, and Sexual Abuse.
Investigators said the 24-year-old victim boarded the train at Franklin Avenue where she encountered the suspect.
She said Cato began to make obscene gestures towards the victim.
She took a picture of him with her cell phone, and then got up from her seat and left the train at the Botanic Garden stop.
She says that Cato followed her and grabbed her buttocks from behind as she climbed the stairs to exit.
She turned around and slapped him in the face causing him to run away.