The trial opened on Sunday of Bahraini human rights activist Nabil Rajab, accused of having "insulted official bodies" in remarks posted on Twitter, a judicial source said.
Rajab, part of the Gulf state's Shiite majority that has demonstrated against the ruling Sunni royal family since 2011, was rejected a request by his lawyer for his release, the source added.
He was arrested in October after posting comments about the interior and defence ministries deemed offensive by authorities.
In one tweet, Rajab charged that Bahrainis allegedly joining Islamist extremists in Syria were originally members of the Sunni-ruled kingdom's security forces.
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"Many #Bahrain men who joined #terrorism & #ISIS came from security institutions and those institutions were the first ideological incubator," he wrote, using one acronym for the Islamic State jihadist group.
Local and international advocacy groups have called for the release of Rajab, who heads the Bahrain Centre for Human Rights.
He was freed in May after serving two years in jail for participating in unauthorised protests.
Rajab had led anti-government marches following a crackdown on Shiite-led demonstrations against the Al-Khalifa ruling family in March 2011.
The judicial source said Rajab's trial will resume on October 29.