The five Shia activists were arrested last Wednesday after asking King Abdullah for permission to form the country's first political party in the monarchy.
Defying a Saudi ban on political parties, the detainees reportedly set up a website for their Islamic Umma Party and wrote to King Abdullah seeking authorization for the move.
Earlier this month, the detained activists issued an initial statement for the party, declaring that the primary aim of the organization was to advance the cause of peaceful political reform.
The arrest of the activists by the US-backed Saudi government comes amid massive popular protests in several other Arab countries where people are demanding greater civil liberties and better living conditions.
"At a time when people throughout the Arab world are out on the street seeking greater freedom, the Saudi secret police seem determined to nip any similar demands in the bud," said a senior HRW Middle East researcher, Christoph Wilcke, in a statement.
The kingdom has only held one set of elections in its history back in 2005. The polls were to pick just half of the members of 178 municipal councils with the rest being installed by Saudi authorities.
Saudi Arabia does not have a parliament and its legislative body is limited to a consultative Shura Council, appointed to offer advice to the ruling king on legal and policy issues.
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