The Alpha Magnetic Spectrometer experiment has detected millions of the particles which may be the first concrete evidence of dark matter particles colliding with each other, they said.
"It's an indication, but by no means is it a proof" of dark matter, Nobel laureate Samuel Ting of the Massachusetts Institute of Technology told NewScientist.com.
The AMS instrument was delivered to the ISS on the final flight of the space shuttle Endeavour in May 2011 to search for dark matter.
Thought to make up about 80 percent of the matter in the universe, dark matter almost never interacts with ordinary matter and so its existence has yet to be conclusively proved.
At a scientific seminar in Geneva, Switzerland, Ting reported AMS has seen more than 30 billion cosmic rays, charged particles of mysterious origin that constantly stream through space.
The telescope's magnetic detector identified 6.8 million of them as electrons or their antimatter counterpart, positrons.
Scientist theorize that if dark matter particles meet in space and annihilate each other, they should decay into electrons and positrons in equal number, raising the overall level of positrons in the universe relative to electrons.
Ting's team found the ratio of positrons to electrons did in fact go up, although the rise is not sharp enough to conclusively attribute it to dark matter collisions.
He acknowledged the positrons could be coming from more mundane sources, like spinning stars called pulsars.
"Our main point is that we published this data, and now let the community work on it," Ting said.