Preheat oven to 375 degrees F (190 degrees C). Grease a 9x5-inch loaf pan.

Whisk flour, oats, sugar, baking powder, and salt together in a bowl. Stir beer and butter into flour mixture using a wooden spoon until dough is well mixed; pour into the prepared pan.

Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 1 hour. Cool bread for 10 minutes before slicing.