Brown spent 2012 with the Sooners after transferring from Penn State in the wake of the Jerry Sandusky scandal.
The 6-foot-3 Brown caught 73 passes for 879 yards and five touchdowns last season. He is the second receiver taken by the Steelers in the draft. Pittsburgh selected Markus Wheaton from Oregon State in the third round.
Brown joins Oklahoma teammate Landry Jones with the Steelers. Pittsburgh took the record-breaking quarterback in the fourth round earlier Saturday.