Combine the brown sugar, paprika, chili powder, dried thyme, garlic powder, salt, and pepper in a small bowl. Stir to mix.

Preheat the air fryer to 380°F for 5 minutes.

Pat the pork tenderloin dry with paper towels. Use a sharp knife to remove the silver skin (the thin silver/white membrane). Rub the spice mixture evenly over all sides of the meat.

Place the pork in the preheated air fryer and cook at 380°F for 10 minutes. Flip the tenderloin and continue cooking for 8-16 more minutes, or until the center of the pork reaches 145°F on an instant-read thermometer. The exact cook time will vary based on the size and thickness of the pork.

Let the pork rest for 5 minutes before slicing and serving.