Irving Fryar's Mug Shot ... After Mortgage Conviction

Ex-NFL superstar Irving Fryar didn't look too happy when he posed for his mug shot to begin his 5 year prison sentence ... after he was convicted of running a mortgage fraud scheme earlier this month.

After he was sentenced on October 2nd, the 53-year-old was taken into custody and eventually wound up at the Central Reception and Assignment Facility in Trenton, NJ ... where he took this mug shot.

As we previously reported, Fryar and his mother were found guilty of conspiring to defraud banks out of more than $1.2 MILLION through a home equity loan scam.

His 74-year-old mom was sentenced to 3 years probation -- in part, because of her age.