The 'Bad Day' band announced their official split last month after 31 years together.
Mills explained that he thinks lead singer Stipe is more likely to work with art and photography instead of making music in the next chapter of his career.
When asked if he expected a Stipe release soon, he told Mojo: "I doubt it. I don't think that's where his passion lies. I think he wants to be in the visual arts.
"I imagine Michael will do a lot of sculpture and photography. I think those are his big interests now."
Mills recently stated that REM are unlikely to ever share a stage together again in the future.
> REM split: Five career-defining tracks - video
Watch REM's video for 'Bad Day' below: