Pegg, 45 and Doug Jung are working on the script for the third instalment of the rebooted franchise, following the departure of Roberto Orci from the project, reported Digital Spy.
"We just want to take it forward with the spirit of the TV show. And it's a story about frontierism and adventure and optimism and fun, and that's where we want to take it, you know," Pegg said.
"Where no man has gone before - where no one has gone before, sensibly corrected for a slighter more enlightened generation."
Chris Pine, Zachary Quinto, Simon Pegg, Karl Urban, Zoe Saldana and Anton Yelchin are all on board to return.
"Star Trek 3" is reportedly being lined up for release in 2016 to mark the 50th anniversary of Gene Roddenberry's science fiction series.