In another bowl combine the flour, cocoa powder, baking powder, baking soda, salt, and sugar. Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.
Bake in the preheated oven for about 20-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.