Harrison's agent, Bill Parise, said the parting is amicable, but Harrison was frustrated with a lesser role in the defense and wants to continue playing.
"There was no animosity or bad feelings. It's just the business of the NFL," Parise told ESPN's Josina Anderson. "I believe he still wants to play. We'll have to wait and see what happens with waivers."
Harrison, 38, has 80.5 sacks in a Pittsburgh uniform, including at least five sacks in each of the past three regular seasons, despite playing a part-time role.
He also came up big in the past two playoff runs, with multiple sacks, but his role decreased this season as the Steelers transitioned to more pass-coverage work for outside linebackers Bud Dupree and rookie T.J. Watt.
Harrison played 40 snaps through 14 games this season, compared with 587 last year.
He signed a two-year deal in March. He keeps himself in excellent shape and could help a team that needs a freakishly strong pass rusher off the edge.
Said Parise: "We'll see what Santa brings us."
Harrison signed with Pittsburgh as an undrafted rookie free agent on April 22, 2002. He's played 177 of his 192 career games for the Steelers, including 107 starts. Over 14 NFL seasons, he's had 788 tackles, 82.5 sacks (two with Cincinnati) and eight interceptions.