The activists, who spoke on condition of anonymity, told AFP on Monday that the people were killed overnight.
The incident came a day after “armed criminal groups” opened fire on Syrian security forces, killing a police officer in the town of Talbisa near Homs.
On Saturday, Syrian President Bashar al-Assad introduced a new package of reforms which he said will meet the demands of the protesters.
Meanwhile, the Syrian president on Thursday issued amnesty for those detained during the protests, aside from those the government considers to have committed criminal acts.
The protests have been held in several Syrian cities since mid-March. Scores of people have been killed during the protests.
Authorities have denied allegations that security forces are responsible for the death of protesters. They blame the violence on armed groups, saying security forces have been given clear instructions not to hurt civilians.
The Syrian government announced earlier in the month that several members of a terrorist group have been arrested and have confessed to shooting people.
Damascus says the protests and the ensuing violence are organized by foreign sources and are aimed at destabilizing the country.