The ceasefire is due to begin at 12 noon (0900 GMT), Reuters cited the so-called Syrian Observatory for Human Rights and al-Manar as reporting.
It applies to the two Shiite villages of al-Foua and Kefraya in Idlib province, and the town of Zabadani and nearby Madaya near the border with Lebanon, they said.
Calm was reported in both areas, they added.
It will be the third time local ceasefires have been agreed in those areas since August. Both previous ceasefires collapsed.