Investigators say it happened at a home on Jaycross Road in Fremont - about four miles southwest of Stantonsburg - around 6:15 p.m.
According to deputies, two brothers were playing with a BB gun in their yard when a 4-year-old shot his brother - 7-year-old Alejandro Mejia - in the chest at close range.
Mejia's parents rushed him to the Wilson Medical Center where he later died.
The sheriff's office says it's treating the incident as an accidental shooting. The case has been referred to the Wilson County Department of Social Services for further investigation.
It's the second fatal shooting of a child involving a pellet or BB gun in North Carolina this month.
An 8-year-old died in Raleigh February 21 when a pellet rifle owned by his grandfather went off - hitting him in the head.