If she isn't spayed then she will be hormonal and more inclined to hump. But if he was neutered properly, his hormones should be pretty much gone at this point, with no chance of making her pregnant. But neutering doesn't get rid of humping behavior entirely, just the hormonal aspect of it. Neutered rabbits will still hump some, as a show of dominance.
If your rabbits aren't bonded and this is something you are attempting, you need to be careful about putting them together, and never unsupervised at first. They are clearly showing dominance issues if they are both trying to do the humping, and in these cases one of the rabbits can easily get irritated with the other and a fight can break out, which in some cases can cause serious injuries.