The Texans released McCain, a sixth-round pick in 2009, last month.
The Steelers need depth at cornerback and they previously met with Chris Owens, who signed with the Chiefs.
In addition to McCain, the Steelers are hosting Moncrief and Baylor running back Lache Seastrunk at their team headquarters.
Moncrief has good size and speed and has been projected to go as high as the second round in May. The 6-foot-2, 221-pounder caught 59 passes for 938 yards and six touchdowns last season and ran the 40-yard dash in 4.40 seconds at the scouting combine.
Moncrief, who declared for the draft after his junior season, is third on Ole Miss, all-time receptions list with 156 career catches.
Seastrunk also declared for the draft following a junior season in which he rushed for 1,117 yards and 11 touchdowns on 158 carries.
The 5-foot-9, 201-pound Seastrunk, a smaller but shifty player, fits the profile of the kind of back the Steelers are likely targeting in the draft to complement Le'Veon Bell and LeGarrette Blount.