The overnight operation at various locations in San Jose also netted more than 400 kilos (880 pounds) of cocaine and 35 weapons.
After being alerted by US anti-drug agents, the country’s Judicial Investigation Organization (OIJ) raided several houses and an armory in three neighborhoods.
Via social media, the OIJ said the detained Colombians appeared to be “part of a FARC cell.”
OIJ spokeswoman Marisel Rodriguez disclosed the cocaine and weapons seizures, adding that a Costa Rican was also arrested in the operation.
The FARC, which is the Spanish acronym for the Revolutionary Armed Forces of Colombia, has about 8,000 fighters under arms and has been fighting the state since its founding in 1964.
The two sides began peace talks in Cuba a year ago in an effort to end Latin America’s longest-running insurgency.