Harrison, the NFL's Defensive Player of the Year in 2008, first went under the knife Feb. 21 to repair a herniated disc. Wednesday's procedure was termed a cleanup.
The Pittsburgh Post-Gazette reported Harrison will need four weeks to recover.
The linebacker indicated in a Facebook post the surgery "went well."
A four-time Pro Bowl pick, Harrison had 10 1/2 sacks, two interceptions and 100 total tackles over 16 starts last year for the AFC champion Steelers.