The 2.5-inch figurine was confiscated on Feb. 10 from the luggage of a man arriving in Oakland from Mexico, U.S. Customs and Border Protection spokeswoman JoAnn Winks said.
The passenger claimed he found the artifact in Ameca, a city in the state of Jalisco in western Mexico, but there were some "inconsistencies" in his story, Winks said.
The man was not detained but agreed to sign a form relinquishing property rights to the item, she said.
Over the past several months, the federal agency has tried to determine the historical nature of the figurine, seeking the help of the University of San Francisco, Stanford University, and the University of Colorado, according to Winks.
Experts determined that the figurine was created by indigenous people in the Ameca area during the pre-Columbian era, meaning it is at least 500 years old, she said.
The artifact is being returned to the Consulate General of Mexico in accordance with a treaty between the U.S. and Mexico for the recovery and return of stolen archaeological, historical and cultural property, Winks said.
The two agencies planned to gather at 11 a.m. today at the Consulate General of Mexico on Folsom Street in San Francisco for a repatriation ceremony.
Carlos Felix-Corona, the Consul General of Mexico in San Francisco, and Richard Vigna, the director of field operations for CBP's San Francisco office, were expected to attend.