The bright object showed up on photos sent to Earth by the rover as it began operations to scoop up some martian soil for analysis, scientists said.
"Yeah, so last night was crazy. When we spotted the object near the rover, we had to quickly come up with a totally new plan," Keri Bean, a meteorologist on the rover team, tweeted Monday.
The rover's scooping operations were temporarily suspended while engineers determined if the fallen object would interfere with sampling activities, Wired magazine reported.
A close-up photo taken with one of the rover's many cameras showed the object was likely a piece of plastic, though it has still not been definitively identified, NASA's Jet Propulsion Laboratory in Pasadena, Calif., said.
Previous Mars missions including the Mars Phoenix Lander and the Opportunity rover have shed small bits and pieces including loose screws, NASA said.