1. Mix brown sugar, corn syrup, peanut butter and salt in large bowl. Microwave uncovered on high 1 minute to 1 minute 30 seconds or until mixture begins to bubble; stir. Stir in popcorn and peanuts until well coated. Let stand 5 minutes.
2. Shape mixture firmly into four 3-inch balls with hands dipped in cold water. Place on waxed paper; let stand about 30 minutes or until completely cool. Wrap in plastic wrap.