Nopperabo is a strange supernatural phenomenon from Japanese folklore. This yokai appears just like any normal human, but it is far from ordinary because it has no face. Generally nopperabo aim to scare unsuspecting victims out of their wits. They lurk around on dark streets, often keeping their backs turned until people get close, whereupon it turns to reveal a featureless face. In some cases it will initially appear with a face, but use one hand to wipe it away, revealing a featureless orb instead.

Nopperabo work in groups, delighting in the terror they cause. When a victim runs from one faceless yokai they find themselves confronted with yet another. Sometimes nopperabo even take the form of family members or friends to really freak their victims out. It is believed that these yokai are actually shapeshifting tanuki, kitsune or, most frequently, mujina (magical badgers). 
From Studio Ghibli film, Pom Poko

The full nopperabo scene in the Studio Ghibli film Pom Poko is worth watching as it is a perfect example of how this yokai operates.