The director explained that the film will have an entirely new cast and a "new direction", but will still build on the three previous movies.
The fourth outing of the franchise will also have a smaller budget than previous instalments, with about $30 million (£19 million) less to spend than Transformers: Dark of the Moon.
"It's not a reboot," Bay told the Los Angeles Times. "That's maybe the wrong word.
"I don't want to say 'reboot' because then people will think we're doing a Spider-Man and starting from the beginning. We're not.
"We're taking the story that you've seen - the story we've told in three movies already - and we're taking it in a new direction. But we're leaving those three as the history. It all still counts... We're moving on to something different."
Bay also hinted that the film may partially be set in space.
"That feels like the way to go, doesn't it?" he said. "I want to go a little off [the planet] but I don't want to go too sci-fi. I still want to keep it grounded."
The director has already said that the fourth Transformers film will be his last.
The movie is scheduled for release on June 29, 2014.
Watch Michael Bay discuss Transformers: Dark of the Moon with Digital Spy below: