The prisoners were found guilty of involvement in al-Qaeda linked terror attacks which killed more than 100 civilians and 71 security personnel, the Saudi newspaper Okaz reported.
The forthcoming executions come as human rights groups expressed growing fears that 21-year-old Ali Mohammed al-Nimr and his uncle could also be executed in the coming days.
al-Nimr was charged with attending a protest, teaching first aid to demonstrators and using his Blackberry phone to urge more people to join in.His sentence prompted strong international criticism, with the French government and a group of UN experts among those calling for a halt to the executions.
Some of the 55 men convicted of terrorism are from Awamiya, a largely Shi'ite town in the oil-producing Eastern Province, where the government has suppressed demonstrations for equal rights.
Diplomats in Riyadh say their governments have been assured Saudi Arabia will not execute Shi'ites convicted after protests.Awamiya residents responded to the news by closing off roads leading into the city with burning debris, local activists said.
The alleged al-Qaeda militants stand accused of attempts to overthrow the government and carry out attacks using small weapons, explosives and surface-to-air missiles, Okaz said.One prisoner was accused of trying to buy nuclear material in Yemen worth $1.5 million for use inside Saudi Arabia.
The charges against the Awamiya residents include sedition, attacks on security officials and interference in neighbouring Bahrain, which has also experienced unrest since 2011.
Saudi Arabia has already executed over 150 people this year, mostly by public beheading, the most in 20 years, rights group Amnesty International said this month.
The Saudi monarchy has in recent years sentenced to death dozens of people convicted of taking part in al Qaeda attacks in Saudi Arabia from 2003-06 and again in 2009.ISIS sympathisers have killed dozens of civilians in Saudi Arabia over the past 12 months with a string of mosque bombings and shootings aimed at members of the Shi'ite Muslim minority as well as security officers and Western expatriates.
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