Fans were turned away from seeing "Joker" Thursday at the Century theater in the 7700 block of Edinger Avenue amid a police presence at the location after officers responded around 5:30 p.m.
Huntington Beach police did not confirm the threat, which was deemed credible, was related to the "Joker" film, saying the decision to close early was made by the movie theater.
Details regarding the threat were not disclosed and no arrest has been made.
Customers who purchased tickets for a 10:30 p.m. showing of the "Joker" were turned away.
"As we were walking in, we see all the police and stuff, it's kinda weird," moviegoer Stephanie Theroux said. "We don't know specifically what it was, we just know something's going on."
As theaters across the country show the R-rated film, which grossed $13 million its opening night, some are increasing security following concerns of threats on social media.
The movie focuses on a man who finds his purpose in committing acts of violence. The movie makes the villain, played by Joaquin Phoenix, the hero and is expected to perform well at the box office.
A new bulletin from the FBI informs law enforcement of unspecified threats against movie theaters showing the film.
"The Los Angeles Police Department is aware of the historical significance and the public concern around the premiere of the 'Joker.' While there are no credible threats in the Los Angeles area, we do
encourage Angelenos to be vigilant," said Jader Chaves of the Los Angeles Police Department.
Some national chains have heightened security and banned masks from being worn by attendees of the psychological thriller.
In 2012, James Holmes who dyed his hair orange to look like the Joker, killed 12 people in a mass shooting at a midnight screening of another Batman movie, "The Dark Knight Rises," in Aurora, Colorado.
The FBI said the threats on social media, which date back to May of this year, are not credible and no specific theaters have been mentioned.
"Increased patrols are essentially just more visibility. Letting the public know that the police are present. That we will be around in the area and to let everybody feel a little more comfortable," Chaves said.