Anti-violence charity White Ribbon has accepted Prime Minister John Key's word that he was unaware of a prison rape joke during an appearance on a music station.

Mr Key joined in a prank on The Rock by getting into a cage and picking up a bar of soap - a reference to rape in prison.

Photo: The Rock

A petition is calling for Mr Key to be axed from his role as a White Ribbon ambassador.

White Ribbon said the jokes were an exercise in bad taste and helped to perpetuate violence by normalising and trivialising it.

However, the charity's campaign manager Rob McCann contacted Mr Key and said it accepted the prime minister's explanation that he didn't comprehend the rape references at the time of the live broadcast.

"When you watch the gag it is very, very quick," Mr McCann said. "We've also seen other gags that are on The Rock and,quite frankly, it's not the type of entertainment we would suggest is great for the culture of New Zealand, there's a lot of misogynistic things that do happen on there."

Mr Key would remain an ambassador for White Ribbon, Mr McCann said.