Our goal was to investigate the efficacy of a Mindfulness-Based Intervention (MBI) in the form of a short-term, online intervention using exercises from Mindfulness-Based Stress-Reduction program on self-compassion, self-reassurance and self-criticism in a non-clinical population. We conducted pre-, post- and two-month follow-up measures of self-compassion, self-reassurance and self-criticism. A total of 146 participants, recruited through convenience sampling, were randomly allocated to the intervention with daily exercises for consecutive 15 days and to a control condition with no treatment. The intervention group reported a significant reduction in self-criticism and self-uncompassionate responding with effects present at two-month follow-up. There was a short-term effect of the training on self-compassion with no effect present at the two-month follow-up and no significant effect on self-reassurance. A limitation of the study is that participants’ previous experience with meditation was not assessed, and thus the findings may be a result of previous meditation practice and not the intervention itself. Despite this limitation, the findings show that an online short-term MBI may be helpful in reducing self-criticism in general population, but a larger study taking into account the limitations needs to be conducted to replicate this effect before recommendations for clinical practice can be made.