Monrovia city spokeswoman Jennifer McLain says fire crews and residents reported bear encounters at least seven times since Sunday.
She says smoke from the smoldering blaze is apparently sending the animals down into residential areas.
Animal control officers are on call to usher the bears back into their San Gabriel Mountains habitat.
Crews working in steep terrain with many sheer drops are digging containment lines around the southeastern flank of the 125-acre burn area. The area is 85 percent surrounded.
Power equipment used by a gardener working in a backyard sparked the fire Saturday.
More than 300 houses were under evacuation orders at the fire's peak.