My dogs are both neutered - however they both still hump people, objects, and even each other. Sometimes they even get aroused.
Is this a sign of dominance? Or is it a sexual thing?
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Sign up to join this communityIt is a sign of dominance.
By mounting other dogs, your dog tries to assert it's dominance, literally being the "top dog" (source: psychologytoday.com).
Also, there may remain some hormone activity after being neutered.
I've personally known a young female dog who was neutered, but kept making "passes" at the housewife, whom she perceived as the pack leader. This behaviour went away over the year that followed.
And, it can happen when the dog is both excited and upset at the same time, feeling conflicted (source: vetstreet.com).
There are a number of reasons why dogs hump, and most of them have nothing to do with sex. As a result, neutering has limited impact on this behavior. The ASPCA gives a fairly thorough list of reasons why dogs hump in an article entitled Mounting and Masturbation. Most frequently, especially in a spayed or neutered dog, mounting and penis crowning are simply signs of over-excitement:
Some dogs respond to stressful or exciting situations by mounting or masturbating. For instance, after meeting a new dog or person, an aroused and excited dog may mount another dog, his owner or a nearby object, like a dog bed or a toy.