Mix together peanut butter and melted butter then, in small batches, mix in powdered sweetener.
Chill the mixture before scooping some of it out, forming it into balls, and placing each ball on top of a parchment paper-lined baking sheet. Chill again until they have firmed up.
Melt the chocolate chips in the microwave. Using a fork, carefully dip the chilled peanut butter balls into the melted chocolate then return them to the baking sheet.
Return the baking sheet to the freezer until the chocolate has solidified.