The four-second clip, filmed from 80 metres above Silicon Valley, California, last year, shows a small white object shoot across the sky past the hovering drone.
The speed of the object appears to rule out insects or dust from air pollution as possible explanations.
Confused Reddit users attempted to make sense of the mystery.
“Even though it's quite a bit of motion blur on the object it appears to have some what of a distinct shape to it,” said Wyldcat.
“Either a disc shape or a wing shape with a cylinder/jet engine on top of it.”
Other users called for freeze frames to be analysed of the shape in order to ensure that they were not being fooled by CGI hoaxers.
“I thought it was a bug at first, but after watching the slow motion video it has to be some kind of military drone or something,” said EducatedHippy.