A number of users noticed games added to their Origin account, such as Dead Space and The Sims, that had been purchased on Steam.
EA revealed this was a test feature, and reassured users that no information was accessed on their computer to transfer the games to Origin.
"A few of you noticed some of your older EA games showing up in your Origin My Games library over the past few weeks, and [we] wanted to clear up any confusion," EA said.
"We tested a feature that in some cases made your older games show up in your Origin My Games Library. At no time was any information on your computer accessed, all of this information was obtained directly from our game registration records. Hopefully we didn't cause too much confusion for anyone.
"We'll be sure to come back and share more information about this feature as soon as we can."
Users can also manually add previously purchased games to Origin through the service's activation tool.
Earlier this year, 11 third-party studios joined Origin to distribute their games. These included The Witcher developer CD Projekt RED and Rift developer Trion Worlds.
An Origin promotion recently ended early that had offered Battlefield 3 free to users who pre-ordered Mass Effect 3 through Origin.
Watch the 'Take Back Earth' trailer for Mass Effect 3 below: