No, it was not real. As far as I know you are not allowed to show real sex on TV in the UK, certainly not at the time this is shown, so it had to be faked, even if you think it looked real.
It's probably happened on occasion that a man or woman has been aroused, but you have to put the scene in the context of how it was shot. It's a very clinical process for the actors involved. They obviously aren't alone, there is the director, camera and sound guys and various other people, never mind all the equipment. Then there's lots of stopping and starting, altering lights, cameras etc, just to get a shot that looks right. Both actors will also have something like modesty patches/pouches. These cover any 'sensitive' areas so that they never actually touch. So, whilst it might appear that they are completely naked, they aren't. I've read in interviews that some even have a small cushion in place as well. Also I've read that several actors find the whole thing funny and not sexy in any way. It seems that some are more worried about cracking up during the scene than anything else, like getting aroused.
Apparently Brad Pitt as a young inexperienced actor cracked a fat on Thelma and Louise in the sex scene. He had to be trained by Geena Davis on how to keep it down.