Interdisciplinary literature indicates different correlates of social media fatigue (hereinafter: SMF). Some studies show that high levels of anxiety may induce lowered Internet use and lead social media users to withdraw from Internet activities. Since the relationship between anxiety and social media use is complex, it is important to investigate mediating factors that may indirectly contribute to or exacerbate this association. Therefore, the main aim of this study is to verify whether fear of missing out (hereinafter: FoMO) is a potential factor accounting for why anxiety is associated with SMF.The research was conducted on a group of 264 adolescents and adults (85% women). The mean age of the respondents was M = 23.76 with SD = 5.98 (range = 14-50 years). The data were collected via online social networking among college students, their family members and friends. The participants answered the Trait Anxiety Scale (TAS), Social Media Fatigue Scale (SMFS), Fear of Missing Out Scale (FoMO), and Revised Life Orientation Test (LOT-R).The outcomes showed that respondents with higher levels of trait anxiety report more intense cognitive, behavioral, emotional, and overall online fatigue. Concurrently, individuals who experience FoMO on the Internet declare being tired of social media use. Moreover, FoMO mediates the association between trait anxiety and all three dimensions of SMF, and its overall result.The present research increases our understanding of the possible role of apprehension related to missing out on the anxiety and fatigue connected to engagement in social media. It is possible to assess that trait anxiety might induce higher SMF when individuals experience a general apprehension that others are doing or having things that they do not.