Spain's Interior Ministry says Abdelmalek Tanem was detained in the southeastern region of Almeria on Wednesday.
Tanem was helping Europeans enter Syria to join extremist groups and fight the Syrian government.
Tanem was a member of the so-called Islamic State in Iraq and the Levant (ISIL) from October 2013 to January 2014, according to the Interior Ministry.
The ministry said in a statement that the 24-year-old Tanem is accused of participating in unspecified terrorist activity in Syria with radical groups operating there and also worked on Syria's border with Turkey to help European would-be extremists get into Syria.
Born in May 1989 in Vitry-Sur-Seine, France, Abdelmalek Tanem, recently returned from Syria.
The arrest is the second Spain has made of an alleged extremist arriving in the country from Syria.
French authorities assisted Spain's Civil Guard with the investigation. The statement says Tanem holds Algerian citizenship.
NTJ/NJF