It might be an "Osnullus", a name which is attached to some large head prosthetics in behind-the-scenes material, but I can't find a primary source connecting the alien we see with that name.
Here is a slightly clearer picture of the character.
Several sites have reported Alex Kurtzman describing the character during a set walkthrough. Scott Collura reported the following from a set visit.
During our tour with the make-up prosthetics department (seen here with Lt. Saru's headpiece and Sarek's ears), we learned that at least two new types of beings will be part of the USS Discovery crew. One is known as Osnullus (he/she/it has a big old alien head) and the other is a synthetic human-like female character called Airiam who works on the bridge of the ship. The goal is to have aliens naturally mixed in with the human characters in the background as well as in the main cast.
Osnullus has been described as a new race for Discovery, and I am not aware of any similar-looking creature in previous shows or movies.
TvGuide mentions James Mackinnon showing off "Osnullus". However, the image used in that piece is of Saru's headpiece.