The Spanish police spokesman said Lopez Pena was one of the main people behind the ending of Eta's ceasefire last year.
The arrest would be the biggest blow against the organisation since the October 2004 arrest in France of its then leader Mikel Albizu.
On the run since 1983, the Spanish interior ministry says Lopez Pena was one of those behind the December 2006 car bomb attack on a car park at Madrid's airport that killed two people and ended a ceasefire declared by the organisation.
Eta announced a "permanent ceasefire" in March 2006 but formally called it off in June 2007 citing frustration with the lack of concessions on the part of the government in their tentative peace process.
Lopez Pena is believed to have taken over Eta's underground political leadership in 2006 when the group was holding peace talks with the government of Jose Luis Rodriguez Zapatero, the then prime minister.
Ainhoa Ozaeta is believed to be the masked woman who read the statement in the June 2007 Eta video officially announcing an end to the ceasefire.
Salaberria, a former regional legislator for Eta's now-banned political wing Batasuna, has been on the run since Spanish authorities for financing the Basque separatist movement.
Suberbiola was a member of Basque independence youth movement close to Eta before going underground.
The arrests follow two car bomb attacks in less than a week blamed on the group.
It was blamed for killing a member of the Spanish civil guard in a massive car bombing last week in a Basque village and it claimed another car bombing on Sunday near Bilbao - the latest in more than 20 attacks by Eta since it ended the ceasefire.
The latest attacks were interpreted as insistence by Eta that it remains a force to be reckoned with and will not be ignored as politicians discuss how to end the region's decades-old conflict.
Since the ending of the ceasefire Spanish and French police have arrested dozens of alleged members of the organisation.
Eta is blamed for killing more than 825 people since the late 1960s in its campaign for an independent Basque state in territory straddling northern Spain and southern France.
Eta, whose initials stand for Euskadi ta Askatasuna, or Basque Homeland and Freedom in the Basque language, is considered a terrorist group by Spain, the European Union and the US.