Heat oven to 350 degrees F. Position a rack in the middle of the oven. Line 18 regular muffin cups with paper cupcake liners.
Mix brownie mix, eggs, oil and water in a medium mixing bowl until well blended. Fill the muffin cups half full with brownie batter. Place about 1 tablespoon chocolate chips in the center of the batter.
Bake 18-20 minutes or until set. Cool slightly. Remove from muffin pans and let cool completely on wire racks.
Stir together frosting and peanut butter in a medium bowl. Spread over top of cooled cupcakes. Using the container of sprinkles included with the frosting, decorate the top of each cupcake.