Rachel Levin, an Al Jazeera producer in Ibiza, said that confusion remains around those who made the threat.
"Several calls were made to a Basque newspaper about the threat. But the caller did not identify himself as an Eta member, which is usually the case."
"Police are still looking for other devices, but they think that that is probably not the case.
"The airport was closed for four hours, leaving hundreds of people stranded on the roadside outside the airport.
"People were pretty surprised to hear the device was found here, in Ibiza. Attacks have nearly always been on the mainland of Spain ... But Spaniards are used to living with this threat."
About 300 flights were scheduled to arrive or depart from Ibiza on Saturday, the first day of the summer holiday season in Spain, which has been on alert since Eta declared an end to a unilateral ceasefire on June 5.
Despite the truce, Eta exploded a bomb at a multi-storey car park at Madrid airport on December 3, 2006, killing two Ecuadorean men in the group's first fatal attack in three-and-a-half years.
Eta had called a "permanent ceasefire" in March last year as Spain's Socialist government inched towards talks on a negotiated settlement to the conflict in the northern region where the group wants to create an independent state.
The Spanish government has held Eta responsible for 819 deaths in the region over four decades,
Last week, Spanish police found a car filled with 130kg of explosives near the Portuguese border which police believed Eta wanted to transport to the southern region of Andalucia for use in a bombing campaign.