He could be. If you feel a strong bond with him you could call him your familiar. You could try casting a circle, meditating, or doing a ritual with him in the room and observe how your dog reacts. Many who believe their pet is also their familiar have mentioned the animal helping or being observant with magickal practices.
Of course, you can also train your pet to join you while meditating or in circle. [Its different for all animals, but dogs are easiest to train] if you decide to have your dog join you, you need to be more observant of him as well. Animals give subtle cues to mood and energy. If you want to meditate but your dog clearly wants to play, work out some energy then try meditating with your pet.
Familiars were originally a myth that witches controlled [or transformed] into animals to do their bidding. Today it has evolved into a belief we share a spiritual bond with the animal. I believe you can have a spiritual familiar, but you can also train an animal to join you in your magickal practice. Some are just naturally more observant of the energy.