Wakanda, the fictional home of Marvel superhero Black Panther, was listed as one of the US' free trade partners on a government website.
The US Department of Agriculture (USDA) had the made-up East African nation on a drop-down menu until this Wednesday.
The gaffe was spotted by Francis Tseng, a fellow at the Jain Family Institute, who posted a screenshot on Twitter.
USDA said it happened during testing and that the entry had now been removed.
Tseng reported later that the listing had been removed from the USDA's list, writing "guess we're in a trade war with them too".
USDA spokesman Mike Illenberg told NBC News in an email that "over the past few weeks, the Foreign Agricultural Service staff who maintain the Tariff Tracker have been using test files to ensure that the system is running properly".
"The Wakanda information should have been removed after testing and has now been taken down," he added.
USDA also tweeted about it, promising that although Wakanda is no longer on the list of US free trade partners, the relationship between the two countries "will always be strong".
Among the commodities listed under Wakanda were live purebred breeding horses, buffaloes, and birds including chickens, turkeys, geese and guinea fowls as well as "live asses".
Vibranium, the metallic substance of extraterrestrial origin and capable of absorbing and storing energy and with which the Black panther's suit is made, is apparently not listed.