Art beads can used to embellish a simple mask for your Halloween celebrations. Here is a very elaborate example from New Zealand bead artist, Joslyn Hobbis.
You could use art bead cabochons, like Joslyn cleverly did for the face of her butterfly. Or add them to a geometric design and bead around them, letting the fabric of the mask show if you aren't up to beading a whole mask.
Another way to add art beads to a mask would be to use it as part of the embellishment on an opera style mask, where a dowel is used to hold the mask in front of your face. Attach your favorite art bead to the top of the dowel. I'd tie some varied fibers under the bead for added texture.
Visit this link for basic information on bead embroidery for art dolls. The directions can be used to embellish a fabric mask, found at hobby stores.