Line a baking sheet with parchment paper.
In a mixing bowl, using an electric mixer, mix together peanut butter and melted butter. In small batches, mix in powdered sweetener. Transfer bowl to freezer to chill for 15 minutes.
After chilling, remove bowl from freezer and, using a spoon, scoop out portion of mixture, form into 1-inch balls using hands, and place atop prepared baking sheet until 16 balls are made. Transfer baking sheet to freezer to chill until balls have firmed, about 20 minutes.
With about 5 minutes left of balls chilling, melt chocolate chips in microwave in 30-second increments.
Remove baking sheet from freezer and, one by one, using a fork, carefully dip balls into melted chocolate, allow excess chocolate to drip off, then return balls to baking sheet. Optionally, use any remaining melted chocolate to drizzle atop chocolate-covered balls.
Return baking sheet to freezer to chill until chocolate has solidified, about 5 minutes.