Buck told Deadline that the writers have not yet discussed how the series will conclude.
"To be perfectly honest, it hasn't come up yet for discussion," he said. "I mean, we're all confident that it will come up. But we're not working toward the end just yet."
He continued: "How you'll wrap is the kind of thing you want to know at least a season in advance, and we haven't discussed it yet at all, so that should tell you something. Everyone will want to check in and they'll all do it with a slightly different idea of what should be done. And we'll definitely hear everyone's thoughts."
Buck also revealed that Dexter's cast and crew are feeling "especially excited and energised and motivated" about the show's upcoming sixth season.
"We skipped ahead a year this season and cleaned the slate, and Dexter is finally done grieving the loss of his wife from the end of season four," he said. "He's largely dealt with that now in season six. He's put it in the past, and we'll now be seeing a stronger Dexter than ever before. And hopefully we won't be killing off any major character this season."
Dexter star CS Lee recently suggested that the new episodes may be controversial, while new cast member Colin Hanks claimed that some events will make fans "flip out".
Dexter will return to Showtime on October 2.
> Dexter season six is darkest yet, says Edward James Olmos
> Read more Dexter coverage
Watch a trailer for the new season of Dexter below: