お面 is read as おめん (omen) and means mask.
おめん
omen
がいめん
outer surface
すいめん
water's surface
おも
face
ばめん
state of the market
つら
cheek meat
ひょうめん
appearances
いちめん
(on) the other hand
しょうめん
front
ほうめん
direction
がめん
screen (of a TV, computer, etc.)
はんめん
half the face
そくめん
aspect