Preheat your air fryer to 400°F (200°C).
In a mixing bowl, combine the ground beef, chopped onion, minced garlic, taco seasoning, salt, and black pepper. Mix well until all ingredients are evenly distributed.
Place the seasoned ground beef mixture into the air fryer basket in an even layer. You may need to cook the beef in batches if your air fryer is small.
Cook the ground beef in the air fryer for 10-12 minutes, shaking the basket halfway through, until the meat is cooked through and no longer pink (internal temperature should be 160°F/71°C).
While the beef is cooking, prepare your taco toppings, such as shredded lettuce, diced tomatoes, and cheese.
Once cooked, remove the beef from the air fryer and set aside. Increase the air fryer temperature to 400°F (200°C) again.
Place the taco shells in the air fryer basket and cook for an additional 2-3 minutes until they are crispy.
Assemble the tacos by filling each shell with the cooked ground beef and adding your choice of toppings. Serve warm with sour cream and salsa on the side, if desired.