Civil Democratic Movement leader Tareq al-Mutairi was detained after he ignored a summons by the public prosecutor's office over a complaint by the Saudi embassy, the interior ministry said on its Twitter account.
It gave no details of the Saudi complaint.
The CDM accused the authorities of kidnapping its leader and said it would hold them responsible for his safety.
It said on Twitter that Mutairi was detained by armed men in civilian dress as he was returning from a meeting of opposition groups.
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On Friday, Kuwait arrested the leader of the Islamist Ummah Party, Hakem al-Mutairi, for allegedly insulting neighbouring Saudi Arabia on television.
He was released on Sunday after questioning by prosecutors.
In recent months, Kuwait has cracked down on online criticism of its Gulf Arab and Egyptian allies.
Authorities have detained several activists and former lawmakers for alleged insults to Egyptian, Saudi or United Arab Emirates leaders.