Use a plate cover that blends in with the mantel color and material to camouflage their appearance. Paint the cover with acrylic paint if you can’t find one that matches exactly.
Install outlet covers in the plug holes to hide their appearance. Press them into place like you would a plug. Only use items that are specifically made for outlets for safety.
Hide the mantel outlets with decorative accessories. Place a potted plant with a hollow bottom on top. Cover the outlets with colorful vases or candles. Put a standing picture frame in front of the outlets.
Drape the mantel in a piece of fabric that covers the entire surface and lends a decorative effect to the space.