Spray insides of 4 microwave-safe mugs with cooking spray. Place 1 teaspoon jelly in bottom of each mug. Combine cake mix and peanut butter with fork in medium bowl; whisk in Reddi-wip and Egg Beaters. Divide batter evenly and place over jelly in mugs.
Microwave each mug individually on HIGH 1 minute to 1 minute 15 seconds or until set. Invert each cake onto a plate. Serve immediately with additional Reddi-wip, if desired.