The two men, aged 31 and 35, were held in dawn raids this morning.
Authorities say the younger of the two used his Facebook account to “spread ISIS propaganda” and show his support for the terror group by facilitating access to its videos.
They also claimed the pair incited worshippers at their mosque to hate non-Muslims and openly praised those who had gone to fight for ISIS in Iraq and Syria.
The mosque was named by Spain’s Interior Ministry as Masslid al Fath.
A spokesman for Spain’s Interior Ministry said: “One of the things that most worried investigators was the influence that both individuals exerted on the members of the Islamic community in Ibiza, highlighting as especially serious the problem of children who went to classes they taught themselves at the mosque.”
The latest arrests bring the number of detentions of suspected jihadists in Spain since 2015 to 156.