yes ... yes it is. Yeast is a fungus which has been used by Man for a long time in the brewing and baking processes.
Unlike most fungi, yeast cells are round or oval in shape. As they grow, yeast cells extend sections called buds which enlarge and eventually become detached, to lead a separate existence.
see http://web.ukonline.co.uk/webwise/spinneret/microbes/fungi.h tm#