"We're kicking it around," Kelley said of the prospect. "If we feel that the material warrants it, we'll do it."
"Everybody's game for getting the band back together, but we want to make sure that we've got the music to justify it," he explained.
"That decision hasn't been made yet, and it'll be story-driven when it is."
"Big Little Lies" is based on the Liane Moriarty novel of the same name, which was adapted as a seven-episode miniseries this year.
Kelley confirmed a second season largely depends on Moriarty, who may have a larger role in future seasons.
"I'm certainly open to it," he said. "I think [Liane], for the book, was game to say, 'Okay, it's your baby. Run with it now.' But she's a great writer, and she also writes excellent dialogue, so if she wanted to jump over to the screenwriting side of the fence, we'd welcome her."
Witherspoon, who played Madeline Mackenzie on the show, previously told E! News a second season is a "possibility."
She reiterated her interest in the project in an interview with The Hollywood Reporter published Tuesday.
"It's sort of up to Liane Moriarty -- she has to figure out if she sees a future for the characters -- but we're definitely open to it," the 41-year-old actress said.
Witherspoon is focused for now on her new TV series with "Friends" alum Jennifer Aniston. The actresses will team on an untitled project focused on a New York morning show.
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