The blood-splattered 15-second clip has no footage from the Showtime series, but it does feature Michael C Hall's eponymous serial killer reciting the cryptic line of dialogue "maybe everything is exactly as it should be".
Luck star Jason Gedrick and Rome actor Ray Stevenson will join the cast for the new season of Dexter, which premieres Sunday, September 30 in the US.
Executive producer Manny Coto has said that Dexter will be "a different show" when it returns, admitting that keeping it fresh is a "terrible challenge".
"It's the hardest thing there is to do," he insisted. "The only way to do it is to overturn the apple cart every once in a while. And let the characters grow and progress and have their lives get overturned."
Hall himself said that "all bets are off" next season and suggested that things will not end happily for his character.
Dexter has also been renewed for an eighth season, which cast member Jennifer Carpenter (Debra Morgan) suggested to Digital Spy could be its last.
Season six currently airs in the UK Fridays at 10pm on FX.