Shearsmith informed his Twitter fans that he and co-creator Steve Pemberton have another idea beyond the dark comedy.
"There really will be no more Psychoville," Shearsmith announced.
"But Steve P and I have 'something else' for you. Only in our minds at the moment."
The BBC Two thriller, which also starred Dawn French and Eileen Atkins, began in 2009 and aired its second series in May this year.
Benidorm star Pemberton had previously indicated to Digital Spy that Psychoville would continue for more episodes.
Asked whether he thought there would be a third series, he declared: "Yes. You never want to get to a point where you think, 'That's it'.
"If we believe the characters are strong enough, which we do, and the storylines are there and people want to spend more time working out these puzzles, we'd definitely like to do more."
> Read Digital Spy's Psychoville interview with Reece Shearsmith and Steve Pemberton
> Psychoville's Halloween special thrills 1.4m