plain face; nondescript face; background-character face
Slang term for a face lacking distinctive features, like an anonymous background character in a crowd. Often used self-deprecatingly or to describe someone who blends in easily.
See also: モブ
Surprisingly many people think they have a plain, background-character face.
彼はモブ顔だから、人混みの中ですぐ見失ってしまう。
He has such a nondescript face that I lose sight of him in a crowd right away.
Compound of モブ (from English 'mob', used in Japanese to mean a background character or extra) and 顔 (face). The term likely arose in online and otaku culture to describe faces that look like generic background characters in anime, manga, or games.