Abdulaziz al-Shubaily, the only founding member of the Saudi Civil and Political Rights (ACPRA) not to be behind bars, was tried in the Specialised Criminal Court, the London-based watchdog said.
He faced a number of different charges which included "communicating with foreign organisations and providing information to Amnesty International for use in two of its reports", the rights group said.
"After shutting ACPRA down three years ago, the authorities have prosecuted and jailed its founding members one by one in a merciless bid to suppress criticism of Saudi Arabia's appalling human rights record," said James Lynch, Amnesty's deputy Middle East and North Africa director.
Lynch urged the kingdom's international allies to "press the authorities to end this iron-fist clampdown on civil society".