The Syrian Observatory for Human Rights said IS beheaded them after accusing them of "photographing sites and handing information to the crusader coalition causing bombing and the death of Muslims".
"ISIS Executed 4 people they Accused them for spying for Coalition," citizen journalist group Raqa is Being Slaughtered Silently (RBSS) said on Twitter, using another acronym for the jihadist group.
RBSS documents abuses in areas under IS control in Syria.
IS has previously carried out several beheadings in Raqa.
And last October, the decapitated bodies of two RBSS activists originally from Raqa were found in the Turkish city of Sanliurfa, 55 kilometres (35 miles) from the border with Syria's Raqa province.
In February, Turkish police identified four IS members as their killers.