Mormon Doctrine, pg. 576; “Three separate personages — Father, Son, and Holy Ghost — comprise the Godhead. As each of these persons is a God, it is evident, from this standpoint alone, that a plurality of Gods exists. To us, speaking in the proper finite sense, these three are the only Gods we worship.” – Bruce McConkie

Exodus 20:3; “Thou shalt have no other gods before me.”

Technically this is called polytheism.  If you believe more than one god exists you are a polytheist.