The British-based Syrian Observatory for Human Rights said Monday's shooting happened in the Khaldiyeh neighborhood of Homs province. Majd Amer, an activist in Khaldiyeh, confirmed the shooting and said several people were wounded.
About 165 Arab League observers are in different parts of Syria to monitor the implementation of a League plan for ending the months of violence.
It was not immediately clear if the observers witnessed Monday's shooting.
On Sunday, the Arab League demanded that the Syrian government immediately stop all violence.
Syria is trying to crush an uprising that erupted in March. The U.N. estimates more than 5,000 people have been killed in the crackdown.
