Anton Garcia and Asuncion Losada advocated an “armed struggle” for the independence of the northwestern Spanish region of Galicia and were detained in the coastal city of Vigo, police said.
The pair, in hiding since 2006, were wanted by the Spanish courts for belonging to a “terrorist organisation” called Resistencia Galega, the Civil Guard said in a statement.
They will appear at the high court in Madrid to face terrorism charges in the coming hours, officers said.
Resistencia Galega was an extreme left-wing group that was active in the 2000s, attacking official buildings and businesses in the finance, real estate and construction sectors.
While not as well known or active as the Basque separatist group ETA, radical groups seeking independence for the remote and rugged Galicia region, which has its own language and distinct culture, have sometimes used acts of violence to promote their cause.
According to the Civil Guard, more than 60 bombings, causing only material damage, were attributed to Resistencia Galega.