The fire was reported around 10:25 p.m. Sunday in the 1100 block of Sonora Avenue, according to the Glendale Fire Department.
AIR7 was over the scene where there was burned damage to a portion of the second floor of the building. Burbank and Pasadena fire departments also responded to extinguish the blaze.
Details about the deaths and what led up to the fire were limited, but detectives remained at the scene of the fire Monday morning.
Police said the fire is suspicious in nature given that it's a commercial building that caught fire in the middle of the night.
Arson investigators and detectives are now working to determine the cause of the fire. An investigation is ongoing.
The identities of the victims have not been released.
No one else was injured in the fire.
A few people who spoke to Eyewitness News off camera said they have businesses in the building.
They said a few of the offices at the location are home, health and hospice related. There's also a photography and videography business, a TV station and a couple of finance businesses.