IntroductionThe non-endemic multicountry outbreak of monkeypox (MPX) has emphasized the issue of conspiracy theories that go viral in times of societal crisis. Now, it is the turn of MPX to join COVID-19 in the conspiracy theory realm. Social media outlets were flooded by a scourge of misinformation as soon as MPX cases began to appear with an evident cross-pollination between diverse conspiracy theories. Given the adverse consequences of conspiracy beliefs, this study aimed to assess the extent of endorsement of MPX conspiracy beliefs among the Lebanese population and to identify its associated factors.MethodsUsing a convenience sampling technique, a web-based cross section was conducted among Lebanese adults. Data were collected using an Arabic self-reported questionnaire. Multivariable logistic regression was performed to identify the factors associated with the MPX conspiracy beliefs scale.ResultsConspiracy beliefs regarding emerging viruses including MPX were detected among 59.1% of Lebanese adults. Participants endorsed particularly the conspiracy theories linking the virus to a deliberate attempt to reduce the size of the global population (59.6%), gain political control (56.6%) or pharmaceutical companies' financial gain (39.3%), in addition to the manmade origin of MPX (47.5%). Remarkably, the majority of surveyed adults exhibited a negative attitude toward the government's preparedness for a potential MPX outbreak. However, a positive attitude was revealed toward the effectiveness of precautionary measures (69.6%). Female participants and those having a good health status were less likely to exhibit a higher level of conspiracy beliefs. On the contrary, divorced or widowed adults, those having a low economic situation, poor knowledge level, and negative attitude either toward the government or precautionary measures were more prone to disclose a higher level of conspiracy beliefs. Notably, participants relying on social media to get information about MPX were also more likely to have a higher level of conspiracy beliefs compared to their counterparts.ConclusionsThe widespread extent of conspiracy beliefs endorsement regarding MPX among the Lebanese population urged the policymakers to find ways to reduce people’s reliance on these theories. Future studies exploring the harmful impacts of conspiracy beliefs on health behaviors are recommended.Supplementary InformationThe online version contains supplementary material available at 10.1186/s40545-023-00580-x.