Probably a recent wheel replacement without resetting the tire pressure monitoring system, or a recent rough encounter with a speed bump or pothole. It sometimes takes some time before a warning pops up. With a flat tyre, response is immediate though (experienced both events in the past with my previous car, not yet with my 1M).
Reset the TPMS. If warning keeps repeating, get it checked. If it stays away, it was only false alarm.
“For ’tis the mind that makes the body rich” (W. Shakespeare, The Taming of the Shrew, Act 4, Scene 3)