Former Cosatu general secretary Zwelinzima Vavi and EFF leader Julius Malema are plotting to overthr.
The poll by the US-based Gallup ranked Mswati among Africa's least popular leaders.
But the government rejected the results of the poll which covered leaders of 34 sub-Saharan nations.
The Swaziland Diaspora Platform, a human rights group based in SA, welcomed the findings, saying they proved that the monarchy was not as loved as it would like the world to believe.
The impoverished kingdom is facing an economic meltdown.