Probably not. Mien is a real word that refers to a person's appearance, or the way someone carries himself or herself. Everyone has a certain demeanor — a characteristic manner that gives insight into an individual's emotions and overall character.
I ran across the word mien in a book. Is it a typo?
Think about someone you've just met. What does the "air" about your new acquaintance tell you? Is their bearing bold or timid? Are they engaging or aloof? Can you get a sense of what's going on inside their heads by their mannerisms and conduct?
Mien appears in many great literary works, including Robert Louis Stevenson's Dr. Jekyll and Mr. Hyde:
The middle one of the three windows was half-way open; and sitting close beside it, taking the air with an infinite sadness of mien, like some disconsolate prisoner, Utterson saw Dr. Jekyll.