Aljazeera's correspondent said the ban, which excluded the Friday speech (khutba) during the noon prayer, aimed at halting what they said was chaos in the mosques.
The Mauritanian security forces have been carrying out search operations in mosques in the capital, Nouakchott, after the arrest of several Islamist leaders and Salafi figures.
The crackdown in the West African country, which straddles black and Arab Africa, comes after the authorities said al-Qaida was recruiting and training Mauritanians to fight in Iraq.
"There are at least 10 mosques which have been searched by the police. They took copies of the Quran," said one opposition source, declining to be named.
No government or police officials were available to comment.
Although an Islamic republic, Mauritanian law bans any party based solely on religion, and analysts say it is one of the most repressive countries in the region towards Islamist movements.
"There are at least 10 mosques which have been searched by the police. They took copies of the Quran"
International Crisis Group said in a report this week Mauritania's attempts to stifle opposition groups by denouncing them as terrorists risked backfiring.
Mauritanian police have arrested scores of Islamic opposition leaders and activists since last month, accusing them of colluding with the Algerian-based Salafist Group for Preaching and Combat (GSPC).
They also accuse Islamist movements of plotting to destabilise the Mauritanian government.