Prepare the brownie mix according to the package directions. Pour batter into a greased 9 by 13-inch pan. Melt the butter in a small saucepan. Add the pecans and sugar and cook, over medium heat, stirring frequently, until the sugar dissolves. Drizzle the caramel mixture over brownie batter and bake until a toothpick can be inserted and withdrawn cleanly, 25 to 30 minutes.