When a cat rubs its head against someone, it's usually to express friendliness. This could be because the cat likes its owner, or it might want to play with it or give it treats. Cats also tend to rub against people a lot during their heat cycle, and this may be accompanied by behaviors such as sticking their rear end up in the air, urinating indiscriminately, and meowing at night.
If you notice your cat not only rubbing itself but also rubbing its head against areas you touch, you should be concerned. This could be a symptom of a skin condition, and you should take your cat to the vet for a checkup to rule out any skin diseases.
