Oncocephala demesai is a species of beetle of the family Chrysomelidae. It is found in Togo.
Adults reach a length of about 5 mm. The head, pronotum and elytra are black with a dark brownish tinge, while the legs are dark brown and the antennae are mostly charcoal black.
No host plant has been documented for this species.
The species is named after the Department of Agriculture Assistant Secretary for Operations Engr. Arnel V. De Mesa.