Last month too, the kingdom arrested and imprisoned dozens of people for the same reasons. The kingdom has been extremely cautious fearing that the conflicts in Iraq and Syria will radicalise a new generation of young Saudis.
Reportedly, the six sentenced on Sunday were also banned from travelling for fixed periods after their release.
Saudi Arabia has banned groups like al Qaeda, Islamic State, Nusra Front, the Muslim Brotherhood, Hezbollah and Yemen's Houthi movement, designating them as extremist.
The country has jailed over 11,000 people for joining these groups or extending moral, material support for them since al Qaeda launched a string of attacks on the country since 2003. Official records show more than 2,500 Saudis outside the country are working with militant organisations.