The Patriots, the defending champions, will meet the Philadelphia Eagles, 27-10 winners over Atlanta, in the Super Bowl at Jacksonville, Fla., on Feb. 6.
Tom Brady passed for 207 yards and two touchdowns while improving to 8-0 in post-season games.
The Patriots turned four Pittsburgh turnovers into 24 points.
Rodney Harrison scored on an interception return and Eugene Wilson made two interceptions for New England, which won the Super Bowl in its last two appearances.
Deion Branch had 116 yards and a touchdown receiving and ran for a TD for the Patriots.
The Patriots avenged a regular-season loss to the Steelers that ended their NFL-record 21-game winning streak.
Rookie quarterback Ben Roethlisberger suffered his first loss as a starter while passing for 226 yards with two touchdowns and three interceptions.