The arrests followed the detention earlier in the week of three Eta suspects in northern Spain and another in southern France.
Rubalcaba said Thursday's arrests "crown a week of police success".
"I think it was a week in which it was shown that the security forces are working day in and day out to do away with the terrorist group Eta and are doing it efficiently," he said.
Last week, Eta was blamed by Spanish officials for a bomb blast that killed a policeman in the Basque Country town of Arrigorriaga, near Bilbao.
The group has killed more than 825 people since 1968, in a campaign for an independent Basque homeland in northwestern Spain and southwestern France.