In a statement released this week, the agency said it had received several reports of rock-throwing on Pacific Coast Highway, between Seapoint Street and Warner Avenue.
The rock-throwing has been happening mostly in the evening - between 6 p.m. and 9 p.m. - but some incidents occurred in the morning, the Huntington Beach Police Department said.
No injuries have been reported, but some cars have sustained damage such as shattered windows and dents.
Two juveniles were arrested in connection with one of the incidents, police said. In other cases, witnesses reported seeing juveniles on e-bikes fleeing the scene.
"Our message is clear: Rock-throwing at moving vehicles is a serious crime," the HBPD said in an Instagram post. "When we catch you, you will be arrested and charged to the fullest extent of the law."
Police said it has boosted patrols in the area.