A spirit animal is traditionally associated with an animal form rather than a human form. That said, it’s also believed that your spirit guide can manifest as anything they’d like to present as. Since spirit guides are non-physical entities, they’re not bound to a static physical form and can appear in many ways.
I recommend diving deeper into spirit animals in astrology because it could also be that a passed on loved one is visiting you as an animal. It’ll be easier to determine if this is the case because their zodiac sign may coincide with the particular animal you feel is your spirit animal.