Authorities said Regulus sat next to a 14-year-old girl on a public bus and made her uncomfortable, making her move toward the front near the driver.
The girl was visiting her grandmother and was on her way home.
Regulus followed her to the front and, when she stepped to the back of the bus to exit in Fullerton, he grinded his pelvis into her rear, prosecutors said.
Off the bus, Regulus grinded against her again, which is his typical M.O., officials said.
The girl pushed Regulus away and he grabbed her arm and pulled her back, Salcedo said.
The girl broke away and Regulus said, "I will find you," Salcedo said.
Regulus had just been released from jail after serving 180 days for a February incident in Costa Mesa.
In that incident, Regulus grabbed a woman's behind while she was inside the Juice It Up! on Harbor Boulevard. He was convicted of touching another person on an intimate part, a misdemeanor.
Investigators in the sheriff's department sex crimes unit recognized Regulus from a bulletin that Costa Mesa police had issued earlier this year and notified them that deputies were looking for him, Salcedo said.
Costa Mesa police started checking Regulus' usual hangouts and found him, officials said.
This is at least Regulus' fifth arrest since 2007 in connection with similar incidents. He is scheduled to be arraigned today and faces up to seven years and four months in prison if convicted on all charges. Prosecutors are seeking to keep him in custody on $100,000 bail.