Local prosecutors said Andrei Klimov was arrested and placed in pre-trial detention following the publication of an article entitled "Revolution Forever, or How to Skin the Gypsy Hog in the Year of the Pig" on the Web site of the opposition United Civic Party.
In the article, the activist claims that President Alexander Lukashenko, dubbed by the United States as "Europe's last dictator," has been involved in the abduction and killing of opposition leaders, and calls for his removal.
Klimov, who has long been known as an outspoken critic of Lukashenko, faced criminal proceedings for alleged slander in 2005.
Earlier, he served a four-year prison term after being convicted of economic crimes, although he maintained all along that his case was politically motivated and prompted by his involvement in a campaign to impeach the president.
International human rights organizations consider Klimov to be a prisoner of conscience.
Last month, Lukashenko said his opponents had no chance of gaining control of Belarus after about 4,000 opposition supporters took to the streets to mark Freedom Day.
"We will not give them the country, and we will hit back at those who have the nerve to roll back current developments," he said.
Lukashenko, 52, won a third term as the post-Soviet nation's president in March 2006.
Opposition activists, led by the losing presidential candidate Alexander Milinkevich, then took to the streets to protest the official result of what they said was a rigged vote, but that rally was soon dispersed and Milinkevich placed in custody.
A fellow presidential hopeful, Alexander Kozulin, was arrested at the end of last year's Freedom Day rallies.
Western powers, including the United States, also called last year's vote fraudulent and introduced travel bans on Lukashenko and other Belarusian government officials, urging them to release political prisoners and improve the country's human rights record.