Hleb transferred from the Gunners to the Barca two years ago, but struggled to make an impact with the Catalans and now concedes he made a mistake in ever leaving the Emirates.
He said: "Of course it is my fault I left Arsenal but this has happened.
"Not a lot of players say no to Barcelona but if I had known before what would happen of course I wouldn't have gone.
"I won the Champions League with Barcelona in 2009 but I didn't play a lot. I lost a bit of my form and confidence."
Hleb turned down offers from elsewhere to move to St Andrews, and the 29-year-old is confident he made the right decision.
He said: "I made a decision to come to Birmingham.
"I decided for one year to come back to the Premier League where I am very happy and want to take this chance."
Meanwhile, Hleb opted against adding fuel to speculation over a possible future move for former Arsenal team-mate Cesc Fabregas to Barca.
He added: "Cesc plays fantastically at Arsenal and is a leader and an important player.
"It is his decision if he wants to stay or leave."