Combine the brown sugar, paprika, dried thyme, garlic, balsamic vinegar, dijon mustard, olive oil, salt and pepper in a small bowl. Stir to mix.
With paper towels, pat the pork dry. Use a sharp knife to remove the silver skin (the thin silver/white membrane).
Brush it all over the sides of the thawed out pork tenderloin. Let it marinate at room temperature for at least 30 minutes, or cover and refrigerate overnight.
Preheat air fryer to 400° F for 5 minutes.
After 5 minutes, carefully place pork tenderloin into air fryer and air fry at 400° F for 20-22 minutes. Internal temp should be 145°. I find if I leave pork in all the way until it hits 145, it tastes dry
The exact cook time will depend on the size and thickness of the pork tenderloin. Let the pork rest for 5 minutes before slicing and serving.
Remove the pork to a plate. Cover and let rest 5 minutes. Cut into slices and serve!