I was seated in the back row on the right side of the aircraft at the window. The movie had just ended and I opened my window blind. I then observed a cylinder-shaped object pass under the plane at approx. 150-200 feet. The object flew under the plane from left to right at a 45 degree angle to the plane. It then made an abrupt slight left turn and flew perpindicular away from the plane but horizontal to the ground until out of my view. The object had a skin that reminded me of the skin of an F 104 from my Air Force days. It was metalic and very shiney. I also did not see any thing that looked like windows on it. It was also very fast.The plane I was on was coming from Atlanta going to Ontario, California and we were still about 1 1/2 hours from landing. I believe we were probably over New Mexico or Arizona.I remember thinking afterward, "oh my God- they are real"!