The incident occurred just before 6 p.m. Saturday in a home at 1410 W Pacific St., NBC News reports.
The boy and his 8-year-old sister apparently found the weapon in a cabinet, when he shot himself in the head, the outlet says.
The girl ran to a neighbor's house and called police.
The boy was rushed to a local hospital and pronounced dead around 40 minutes after the shooting.
Click here to follow Daily Voice Reading and receive free news updates.