In a large bowl, combine cereal, peanuts and marshmallows. In a microwave-safe bowl, melt chocolate and peanut butter on High for 1 minute and then in 30 second intervals until fully melted. Stir chocolate into cereal mixture. Mixture will be slightly runny. Drop by tablespoons onto waxed paper. Let set until firm, 2 hours. Store in an airtight container.