0900 GMT April 19, 2018
More than 60 prominent clerics, writers, journalists, academics and activists are reported to have been detained in a wave of arrests since September, they said in a joint statement, Reuters reported.
The crackdown on dissent has been denounced by Amnesty International and Human Rights Watch, but strong criticism by the UN of the oil giant is rare.
Riyadh says it does not have political prisoners, but senior officials have said monitoring of activists is needed to maintain social stability.
"We are witnessing the persecution of human rights defenders for peacefully exercising their rights to freedom of expression, assembly, association and belief, as well as in retaliation for their work," the five independent experts said.
They decried a "worrying pattern of widespread and systematic arbitrary arrests and detention" through the kingdom's use of counter-terrorism and security-related laws.
Prominent preacher Salman al-Awdah, whom the UN experts described as a "reformist" and an influential religious figure who has urged greater respect for human rights, is among those held, they said.
They also named academic and writer Abdullah al-Maliki, entrepreneur Essam al-Zamel, and Abdulaziz Al Shubaily and Issa bin Hamid al-Hamid of the banned Saudi Civil and Political Rights Association as detainees.
"Despite being elected as member of the Human Rights Council at the end of 2016, Saudi Arabia has continued its practice of silencing, arbitrarily arresting, detaining and persecuting human rights defenders and critics," the experts said.
The UN investigators have global mandates on arbitrary detention, human rights defenders, the right to freedom of opinion and expression, freedom of religion or belief, and protection of human rights while countering terrorism.
The statement did not mention the arrests in November of some 200 princes, ministers and business leaders who were then held in the luxurious Ritz-Carlton hotel in what Riyadh said was a crackdown on corruption. Some have since been freed after they reached financial settlements with the government.