expression
deadpan face; expressionless face; po-faced
Describes a face as blank and emotionless as a Noh mask. Often used for someone hiding their feelings or showing no reaction.
彼は能面のような顔で、何を考えているのかわからない。
With his deadpan face, I can't tell what he's thinking.
彼女は能面のような顔でその知らせを聞いた。
She heard the news with an expressionless face.