Rinna detailed the nerve-wracking experience on Twitter.
"We had the most terrifying phone call happen today. People should be aware of these scam terrorists calling saying they have your child," the 52-year-old actress and reality star wrote in a series of tweets. "They put a child crying on the phone saying mom help me please and then they try and extort money and say they will kill your child. It is the worst scariest nightmare and it must stop now."
The actress, who was filming Real Housewives on Tuesday, added that her two daughters, 17-year-old Delilah and 14-year-old Amelia, were OK and unharmed.
"Thank god my girls are ok and it was a terrorist hoax," she wrote. " I think information is power. That is why I am sharing this. I am still traumatized, but I don't want this to happen to anyone else."
It's unclear if Rinna was specifically targeted or if she was chosen at random by the by scammers.
Rinna stressed that she had contacted the police and the FBI and that they were "now involved." The Beverly Hills Police Department and the FBI said they were not aware of the situation at time of publishing when ET reached out.