Make sure the coffee grounds are dried out. If they are still damp, spread them on a baking sheet and place in a 350-degree-F oven until just dry, 6 to 10 minutes. Remove from the oven and let cool.
Place the coffee grounds and peppercorns in a spice grinder and grind until the pepper is coarse. Pat the steaks dry with a paper towel and sprinkle liberally with salt. Sprinkle generously with the rub, making sure to coat the steaks well. Press the rub into the steaks.
Heat a cast-iron skillet over medium-high heat until hot and add the oil. Add the steaks and cook until a nice crust forms and the steaks are cooked to your liking, about 4 minutes per side for medium rare.