Preheat oven to 375 degrees F (190 degrees C). Lightly grease a 9x5 inch loaf pan.
Beat the beer and brown sugar together in a mixing bowl to make a smooth mixture. Add the baking powder, and gradually stir in the flour to make a smooth dough. Pour the batter into the prepared pan.
Bake in preheated oven for 40 minutes.
Remove the bread from the oven, and pour melted butter over the top. Return to the oven, and continue baking until a knife inserted in the center comes out clean, about 10 minutes more. Cool in pan 5 minutes before turning out onto a rack. Cool bread 10 minutes more before slicing.