The protesters marched on Thursday from the Ras al-Romman mosque towards parliament to press for the release of Abdul Hadi al-Khawaja, who is standing trial on charges of "inciting hatred against the regime".
The demonstrators also demanded the resignation of Prime Minister Khalifa bin Salman al-Khalifa.
The rally passed without incident.
Earlier on Wednesday, lawyers for al-Khawaja charged that his trial was a breach of constitutional provisions on freedom of speech.
Al-Khawaja, vice-president of the Bahrain Centre for Human Rights, was arrested in September and his organisation closed down on the grounds that its activities violated the Gulf state's associations law.
Prior to his arrest, he had addressed a poverty symposium at which he made remarks critical of the government's management of the national economy.
He also faces charges of "propagating rumours accusing government officials and the government of abuse of power".
He pleaded not guilty at the start of his trial last Saturday.
The next court hearing has been set for 25 October.