The whole Cabinet underwent checks for cornavirus on Thursday as the minister for Equality, Irene Montero, announced that she had tested positive.
Her partner is Pablo Iglesias, leader of Unidas Podemos and a deputy prime minister. He immediately went into quarantine.
On Tuesday, Congreso (lower house of Spain's parliament) cancelled virtually all of its activities after an MP tested positive for coronavirus.
The far right Vox party announced that Javier Ortega Smith, its second in command, had the virus and apologised for not cancelling the party conference attended by 9,000 people at the weekend in Madrid.
The party has said that out of "responsibility" it has sent its 52 MPs to work from home. On Wednesday, another Vox MP tested positive.
A third MP, Ana Pastor, also tested positive on Wednesday. Pastor had recently attended a Women's Day event in Malaga city.