Who knows? If it doesn't hurt or impede your movement any, wait and see. If it starts to hurt or impede movement in any way, might be time for an exam. There is a tendon there that is a common problem as you age if you're very active, the patella tendon. Ever seen all those folks at the gym with that thin strap underneath their knee? That's for patella tendon pain.
An accurate diagnosis requires clinical history and physical examination.
You should see your doctor for further workup and evaluation.
Consider entities such as iliotibial band syndrome:
It might be a good idea to rest and avoid any activities which trigger the pain for at least 6 weeks.