The 25-year-old left St James' Park for the Scottish outfit on a permanent deal following two loan seasons at Parkhead, but Forster has revealed that a lure to the Premier League could be too strong to reject.
"I'd like to go back to Newcastle at some point, if the opportunity arises," Sky Sports News quotes Forster as saying.
"I'm a Newcastle fan and I've got unfinished business there. It was a wrench to leave, it's my hometown club. But it wasn't meant to be.
"Everyone wants to be playing in the Premier League. It's the place to be. At the minute I'm very happy at Celtic and playing Champions League football, but long-term it would be nice to play in the Premier League."
With regards to Forster's international future, the goalkeeper received his first call-up to the England squad under manager Roy Hodgson last year.