The show on June 12 has resulted in more than 600 complaints in the past seven days.
634 viewers in total have objected to the highlights show which began with a warning about 'risky sexual activity'.
In the scenes that followed, broadcast after 9PM, Laura Carter was seen strangling and whipping Marco Pierre White Jr with a belt before he sucked her breasts in the garden.
Later the two hit the bedroom and had sex under the covers with their fellow housemates next to them.
"We're investigating whether sexual scenes in this episode of Big Brother exceeded generally accepted standards for its time of broadcast," said Ofcom in a statement today.
Marco became the first housemate to be evicted from the series last Friday and revealed today he and his fiancée had called off their engagement following Big Brother.
He admitted he may have pushed things too far on the show and explained: "I'm in contact with her at the moment, I just spoke to her and I think we've decided to just see how it goes over the next couple of weeks and just be friends for the moment," he explained.
Big Brother continues nightly on Channel 5.