Pat the beef tenderloin dry with paper towels.
Use kitchen twine to tie the roast evenly and tuck the tail under so it has a uniform shape for even cooking.
In a small bowl, combine black pepper, salt, garlic powder, red pepper flakes, dried thyme, and mustard seed.
Brush the tenderloin all over with the olive oil, then press or dredge the spice mixture onto all sides until evenly coated.
Preheat the grill to high heat and oil the grate to prevent sticking.
Place the tenderloin on the hot grill, cover, and brown on all sides, rotating every 4 minutes or so to develop even color; continue grilling until an instant-read thermometer inserted into the thickest part reads 130°F for medium-rare.
Transfer the meat to a cutting board and let rest for 15 minutes before slicing against the grain and serving.