Mohamad al-Bajadi was detained in March 2011 after tweeting in support for families demonstrating outside the Interior Ministry in Riyadh demanding the release of jailed relatives, according to fellow activists.
Al-Bajadi is a co-founder of the Saudi Civil and Political Rights Association (ACPRA).
Amnesty International condemned the detention as a violation of freedom of expression, referring to al-Bajadi as a possible "prisoner of conscience."
A letter smuggled out of jail declared that he had begun a hunger strike in protest at his detention without trial.
But an Interior Ministry spokesman denied on Tuesday that al-Bajadi, who has been prevented from seeing his family since his incarceration, was refusing to eat.
"Mohamad al-Bajadi did not go on hunger strike and he is in good health, consuming food on a regular basis and in the company of other inmates," ministry spokesman Mansour al-Turki said.
Mohammad al-Qahtani, al-Bajadi’s lawyer, on Wednesday slammed the government claim as a "lie," saying that sources inside the prison had confirmed the hunger strike was ongoing.
"Obviously they are not telling the truth and it is business as usual. They are not held accountable for the information they are giving out," he told Al-Akhbar.
"We have a document written by his own hand that he went on a hunger strike on March 11. We have unofficial communication with him – there are people who visit the prison and have contact with him."
Al-Qahtani, who has been prevented from visiting the prison to visit his client, called on the Saudi government to try al-Bajadi in public.
"If they are telling the truth so be it – open your prison for inspection. We are demanding them to try him in an open court, that is all that we are asking."
Saudi Arabia is an autocratic monarchy that has no elected parliament and zero tolerance for public dissent.
Pro-democracy activists in the country’s oil-rich Eastern Province have been suppressed since protests broke out last year.
Independent rights groups estimate that the number of prisoners in Saudi Arabia ranges between 12,000 and 30,000, but the Interior Ministry denies there are any political prisoners in the kingdom.
