The Human Rights Protection Party organised the rally to highlight judicial decisions it sees as flawed and against the Constitution.
The Samoa Observer reports the arrests were confirmed by Assistant Police Commissioner Auapa'au Logoitino Filipo who also said more arrests will be made as investigations continue.
He said the investigation is also looking at another roadblock at Sasina village and arrests are likely from there.
The arrested pair are facing charges for disorderly conduct in public places.
Opposition leader Tuilaepa Sailele Malielegaoi said at the time he turned the convoy of close to 100 vehicles for safety reasons after gunshots were heard at the Salelologa roadblock.
Men at Sasina were seen on social media videos standing behind rocks lined up across the public road making threatening statements towards Tuilaepa and HRPP.
Deputy Commissioner Papali'i Monalisa Keti said social media posts are being used in their investigations to identify perpetrators.
Photo file Loop Samoa Caption: Samoa Police