Positive mental health is considered to be a significant predictor of health and longevity; however, our understanding of the ways in which this important characteristic is represented in users’ behavior on social networking sites is limited. The goal of this study was to explore associations between positive mental health and language used in online communication in a large sample of Russian Facebook users. The five-item World Health Organization Well-Being Index (WHO-5) was used as a self-report measure of well-being. Morphological, sentiment, and semantic analyses were performed for linguistic data. The total of 6,724 participants completed the questionnaire and linguistic data were available for 1,972. Participants’ mean age was 45.7 years (SD = 11.6 years); 73.4% were female. The dataset included 15,281 posts, with an average of 7.67 (SD = 5.69) posts per participant. Mean WHO-5 score was 60.0 (SD = 19.1), with female participants exhibiting lower scores. Use of negative sentiment words and impersonal predicates (“should statements”) demonstrated an inverse association with the WHO-5 scores. No significant correlation was found between the use of positive sentiment words and the WHO-5 scores. This study expands current understanding of the association between positive mental health and language use in online communication by employing data from a non-Western sample.