Ross Township (Pa.) police cited Brown on Nov. 8 for the infraction. He was found guilty Tuesday in Pittsburgh, according to Allegheny County district court records.
Brown was fined more than $400.
Police told WPXI-TV and the Pittsburgh Post-Gazette that officers were searching for a bank robbery suspect when they pulled over Brown while he was driving a black Porsche in excess of 100 mph on Nov. 8.
The Steelers beat the Carolina Panthers 52-21 hours later at Heinz Field in Pittsburgh, with Brown making six catches for 96 yards and a touchdown.
Brown, 30, has been rumored to be wanting a split from the Steelers this offseason. The sixth round pick in the 2010 NFL Draft led the NFL with 15 touchdowns in 2018. He has six consecutive seasons with at least 1,200 receiving yards and 100 receptions.
He is due a $2.5 million roster bonus on March 17 and has a base salary of $12.6 million in 2019. Brown signed a four-year contract with the Steelers in 2017.