The boy was playing with his 5-year-old brother upstairs in their home in the 100 block of Bailey Road when he somehow got pushed through a screen and out the window, Lee said.
A neighbor heard the toddler crying and alerted family members, who called for emergency help at about 2:50 p.m.
When sheriff's deputies and Contra Costa County Fire District paramedics arrived, they found the boy conscious and alert. He had a bruise on his head from the fall, but appeared to have been saved by the bush.
He was taken to Children's Hospital in Oakland as a precaution, Lee said.
Investigators do not believe any malicious intent or parental negligence led to the boy's fall and the incident is not under investigation, Lee said.
"Obviously it was an accident," Lee said. "It was two young boys playing and one of them ended up going out a window."