Anderson, 34, said in a statement she contracted the disease by sharing a tattoo needle with her estranged ex-husband, Tommy Lee.
"He never disclosed it to me during our marriage," she said.
Anderson, who has also starred in the television series "Baywatch," is locked in a bitter custody battle with Lee, a former drummer for Motley Crue, over their two young sons.
A spokeswoman for Lee, 39, dismissed Anderson's statement
"Hopefully she will realize that she is only doing more harm to her children and herself by trying to use the media as a tool to hurt Tommy and their two boys," publicist Beth Katz said.
Meanwhile, Anderson's boyfriend, Kid Rock, said Thursday he didn't know she had hepatitis C.
"I was with her last night and she didn't really release that statement to me or say anything about it. She's fine," the rapper-rocker said during an appearance on "The KTLA Morning News."
"There's so much going on with the situation she's in that I really don't want to talk about. I think a lot of people try to say things that are very hurtful," said Kid Rock, whose real name is Bob Ritchie.
About 3.9 million Americans have hepatitis C, which is spread through blood-to-blood contact, sharing needles for intravenous drug use or unprotected sex, according to the Centers for Disease Control and Prevention.
It can cause jaundice, fatigue, pain and vomiting and gradually affects the liver, leading to cirrhosis and liver cancer.
About 8,000 to 10,000 people in the United States die each year from complications due to hepatitis C infection.
An antiviral drug is one of the standard treatments, and therapy is successful about half the time.