Preheat the oven to 200 degrees . In a large bowl, toss together the popcorn, peanuts and pumpkin seeds.
In a medium saucepan, melt the butter over medium-high heat. Whisk in the brown sugar and cayenne until bubbling and thickened, 2 to 3 minutes. Pour over the popcorn mixture; toss to coat. Season with salt and black pepper.
Transfer to a foil-lined baking sheet. Form small clumps of the popcorn mixture and bake until toasted, 40 minutes. Let cool completely.