Preheat oven to 400 degrees F (200 degrees C). Grease 16 muffin cups.
In a large bowl, mix the whole wheat flour, millet flour, baking powder, baking soda, and salt. In a separate bowl, mix the buttermilk, egg, vegetable oil, and honey. Stir buttermilk mixture into the flour mixture just until evenly moist. Transfer batter to the prepared muffin cups.
Bake 15 minutes in the preheated oven, or until a toothpick inserted in the center of a muffin comes out clean.