The 50-year-old singer tweeted on Saturday that "there won't be any more from BZ" amid rumours of a reunion for the group's 30th anniversary in 2023.
Gately died in 2009, shortly after the band got back together, but the remaining members have not performed together as a four-piece since their Thank You & Goodnight farewell tour came to an end in 2019.
Graham added: "Thankfully BZ was laid to rest in 2019 before any more damage could be done to its legacy after our beloved Stephen passed away."
Hi folks.Sorry its been a while.Anyway. Sadly there won’t be any more from BZ.
No BZ30..But thankfully BZ was laid to rest in 2019 before any more damage could be done to its legacy after our beloved stephen passed away.I’m of the opinion that was the time we should have finished
— Mikey Graham / Boyzone (@MRMIKEYGRAHAM) November 19, 2022
Graham said in conclusion that he was "of the opinion" that the group "should have finished" in the wake of Gately's passing.
Keating said he has "a great relationship" with the other members of the group and suggested they will likely meet for dinner to mark the 30th anniversary.
"I’ve never been able to come to terms with the band as a four-piece. It’s never worked for me. I miss [Gately] when I’m on stage," said Keating.
He added: "So for me, we went out on a high after 25 years. We wrote that final chapter. We did a world tour."
Boyzone were formed by Louis Walsh in 1993 and subsequently released seven studio albums, selling more than 25 million records worldwide.
Read more: Ronan Keating pays tribute to Stephen Gately
Their first four albums all went to number one in the UK charts and the group also clocked up six UK number one singles over the course of their time together, including No Matter What.
In 2018, they released final album Thank You & Goodnight and dedicated its release to Gately.
Watch: Boyzone once planned to do a reality TV show together