Firefighters responded to a neighbor's report of a blaze at 319 Drayton Court at 2:25 p.m. today, district Battalion Chief Ben Smith said.
Arriving crews found smoke throughout the two-story, four-bedroom house, Smith said.
They located the blaze in a rear bedroom of the home, which is also where they found an elderly man who lived in the house, Smith said.
Firefighters put out the fire at about 2:50 p.m. and the man was pronounced dead at the scene. They found his cat that had also died in the incident, Smith said.
The fire was contained to the one bedroom, but the smoke and flames destroyed more than $20,000 worth of damage to the house, Smith said.
The man's name has not been released by the Contra Costa County coroner's office, and the office will determine his cause of death, Smith said.
The cause of the fire is still under investigation.
No other injuries were reported.