Smith was recently hired as a defensive co-ordinator for the Carver High School varsity football team.
The Birmingham News reports the 35-year-old was let go after a reporter asked the school about Smith's criminal record.
Smith was granted full parole in 2009 after serving almost two years of a six-year sentence for knowingly exposing two women to HIV.
The school's initial background check of Smith covered the United States, but not other countries including Canada.
There was no reaction from Smith in the Birmingham News story.
Carver High School's football coach Billy Culver also resigned this week, although a school official says it was unrelated to Smith.