Many people were posting on social media about the sight, concerned that perhaps the plane was being shadowed by a fighter jet over security concerns.
Not to worry.
In fact, officials at Ontario Airport say the Lear jet was simply capturing some video footage of the UPS plane for marketing purposes.
Flight tracking websites show the delivery company's plane flew from San Bernardino, headed west to the coast and over the Channel Islands then turned around and landed at Ontario, for a total flight just under 500 miles, lasting almost 90 minutes.