Theaters, such as AMC and Landmark, will allow moviegoers to wear costumes but not masks or face paint.
Part of the fear over the movie comes from the shooting at a previous "Batman" film in Aurora, Colorado, where 12 people were killed.
Tina Coon's son was killed in the 2012 shooting.
"I think it's sad that people react to a fake story and make it real," said Coon.
"Joker" actor Joaquin Phoenix says it's not the filmmaker's responsibility to teach morality.
"If you have somebody that has that level of emotional disturbance, I think that they can find fuel anywhere," said Phoenix.
The movie is reportedly set to break October release records, and some people say the controversy may generate more curiosity and ticket sales.