Moroccan media including the public television channel 2M reported the arrests after the incident in the kingdom's economic capital Casablanca.
In the footage posted yesterday, six bare-chested teenagers are seen assaulting a weeping young woman and laughing as they touch her private parts.
The half-stripped victim is seen crying out in distress as no passenger intervenes to help her and the bus fails to come to a halt.
The latest incident comes less than two weeks after footage of men hounding a young woman walking alone in the northern city of Tangier was shared widely on social media, sparking a heated debate in the North African country.
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Media headlines included "Horror in Casablanca" and "Monsters commit an odious crime" as reports focused on the phenomenon of women being harassed in public places.
There were calls for the perpetrators of the bus attack to be brought to justice, and for a Casablanca sit-in on Wednesday.
Official figures show that nearly two-thirds of Moroccan woman have suffered violent attacks, often in public places.