Preheat the air fryer to 400°F (200°C) for 5 minutes.
Pat the salmon fillets dry with paper towels.
Brush both sides of each salmon fillet with olive oil.
Season the salmon fillets evenly with salt, black pepper, and garlic powder.
Place the salmon fillets skin-side down in the air fryer basket, making sure they do not overlap.
Cook the salmon in the air fryer at 400°F (200°C) for 10 to 12 minutes, or until the salmon flakes easily with a fork.
While the salmon cooks, prepare the mustard sauce by combining Dijon mustard, whole grain mustard, honey, and lemon juice in a small bowl. Mix well until smooth.
Once the salmon is cooked, carefully remove it from the air fryer and transfer to serving plates.
Drizzle the prepared mustard sauce evenly over each salmon fillet.
Serve immediately with your choice of sides.