Footage of the incident showed Roberts trailing a paparazzo in her car and persuading the driver to pull over so she could talk to him with his camera off.
Roberts told "Access Hollywood" in an interview why she dressed the man down.
"I just told him a school is not a place for a grown man to be crawling around trying to take pictures. It's not where you come to take pictures of me," Roberts said. "He's looking like a pedophile, so somebody is going to call the police on him and land him in jail. If you want to take a picture of a person, then go to an adult place. Go to the coffee shop, go to the grocery store, go to the restaurant. Don't stake out someone's children's church, school or playground environment."
Roberts will next be seen opposite Tom Hanks in the "Charlie Wilson's War."