The blast happened on Thursday afternoon in the al-Qa'tour district of the port city of Latakia.
Syrian state news agency Sana said a motorcycle bomb was responsible.
Syrian state TV channel Ikhbariya said it happened as people were leaving prayers. It was not immediately clear how many casualties there were from the bomb, or who carried it out.
Latakia lies in a coastal region that is home to President Bashar al-Assad's extended clan. Until recently, it had been largely spared the violence that has engulfed much of Syria during the civil war.
But dozens of people were killed in nearby cities last month in bombing and other attacks which were carried out by the so-called Islamic State group (IS).
A bomb has exploded near a mosque in a Syrian coastal city, killing and wounding several people.