Preheat the air fryer to 400°F (200°C) if needed.
Pat the salmon dry with paper towels, especially the top and sides. This helps the topping stick and brown.
In a small bowl, mix the mayonnaise, oregano, lemon juice, salt, and black pepper until smooth.
Spoon the mixture on top of each salmon filet and spread into a thin, even layer. Only the top needs topping.
Lightly spray the air fryer basket with olive oil if it tends to stick. Place salmon in the basket with space between each piece. Cook in batches if needed (many air fryers fit 2 filets best).
Air fry at 400°F (200°C) for 8 to 10 minutes (start checking at 8 minutes). Salmon is done when the sides look opaque and it flakes easily with a fork. Add 1 to 2 minutes if needed.
Remove with a small spatula and let rest for 1 minute. Add a few extra drops of lemon before serving if you like.