A 28-year-old woman has been charged after she allegedly indecently assaulted a police officer by grabbing his genitals in the CBD on Saturday night.

About 7.45pm, police were arresting a person on Wellington Street when they were approached by the woman, who is said to have indecently assaulted the male officer.

She was arrested on the scene and charged with assaulting a public officer.

It is not clear whether she knew the person who was being arrested prior to the incident.

She will appear in court next month.