Fear of missing out (FoMO) involves the desire or urge to stay continuously connected to and kept up-to-date with a social reference group. The present study explored the relationships between adult attachment and FoMO and the potential mediating effect of a mindful attitude. The present study was carried out on 192 participants (meanage = 23.24 years; SDage = 4.33 years), of whom 151 (78.6%) were female and the remaining 41 (21.4%) were male. The participants completed the Adult Attachment Scale—Revised (AAS-R), which evaluates Close, Depend, and Anxiety attachment, the Cognitive and Affective Mindfulness Scale—Revised (CAMS-R) and the Fear of Missing Out Scale (FoMOs). The results indicated that the three forms of adult attachment (Close, Depend, and Anxiety) were associated with FoMO through the indirect effect of mindful attitudes. This study yielded relevant theoretical and practical implications regarding the critical role of a mindful attitude as a protective factor against FoMO. Limitations and future research directions were also discussed.