Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said three buses carrying about 150 civilians had left the district and more were to follow.
The deal was reached earlier this month and will see some 2,000 rebels and their families leave the besieged Waer district of Homs city, once dubbed "the capital of the revolution".
Abdel Rahman said about 750 people, including civilians, were awaiting evacuation today.
Buses would head from Homs city to the Qalaat al-Madiq area of central Hama province, then onto the northwestern province of Idlib, he added.
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Idlib province is held by the Army of Conquest rebel alliance, which includes Al-Qaeda affiliate Al-Nusra Front and which would send some of its forces to escort the buses, according to Abdel Rahman.
Earlier this month, Homs governor Talal Barazi said all rebels would leave Waer within two months, in return for the regime lifting its siege of the district and ending military operations there.