Arturo Villanueva Arteaga, a 32-year-old Basque activist who has lived in west Belfast for four years, was arrested in a raid on April 21.
He was arrested under a European warrant issued by the Spanish authorities seeking his extradition to Spain on "terrorism" charges.
The Basque people, whose nation straddles the Spanish and French borders, have waged a long struggle for self-determination from Spanish rule. Most of the 3 million Basques live within the Spanish state.
Villanueva is well-known in the west Belfast community, where he runs a tourism business. He intends to fight the extradition attempt.
He was released on bail under conditions of reporting to police daily and submitting to a 9pm curfew. The extradition hearing to begin on May 13.
The Belfast Basque Committee, which held a protest outside the court, has called for the case to be dropped.
A spokesperson said: "Arturo has been living openly in Belfast for four years and has a life here. We are calling for the immediate dropping of this case and an end to the repression of Basque civil society."
The charges relate to Arteaga's alleged involvement in the pro-independence Basque youth organisation Segi, which was outlawed in 2001 and declared a "terrorist" organisation by the Spanish Supreme Court in 2007.
If the extradition is successful, Villanueva faces up to 14 years in prison.
In 2001, Villanueva was among 17 young people charged with being a member of the group.
Segi is an independent socialist youth organisation with thousands of members. It organises political campaigns on the right to Basque self-determination, as well as social and economic issues affecting youth.
Released on bail, Villanueva did not attend the political show trial.
In 2005, Spanish prosecutors called for Villanueva to be sentenced to 14 years' jail in his absence.
The proscription of Segi by the Spanish government was part of the state's long-standing policy of criminalising virtually all political parties, media sources and civil society groups in favour of Basque self-determination — jailing members of those organisations.
In December, UN human rights special rapporteur Martin Scheinin said Spain's Law of Political Parties defined "terrorism" so vaguely that it "might be interpreted to include any political party which through peaceful political means seeks similar political objectives" as those pursued by armed organisations.
Villanueva's arrest comes after the Belfast Recorder's Court in March ruled in favour of a Spanish extradition request for former Basque prisoner Inaki de Juana Chaos to face charges of "glorifying terrorism".
De Juana is appealing the ruling on May 15.
The Basque Committee is urging the local community to oppose the targeting of Belfast's Basque community by the Spanish authorities and to support Villanueva and de Juana in their fight against extradition.
[Reprinted from An Phoblacht, the newspaper of republican party Sinn Fein.]