To what extent meditation techniques (which incorporate practices to regulate attention, construct individual values, or deconstruct self-related assumptions), are more or less effective than relaxation therapy in the treatment of anxiety, is not clear. The aim of this study was to examine the effectiveness of meditation compared to relaxation in reducing anxiety. A systematic review from PubMed, Embase, PsycInfo and the Cochrane Central was conducted. A meta-analysis of 14 RCTs (n = 862 participants suffering from anxiety disorders or high trait anxiety) was performed. Effect sizes (ESs) were determined by Hedges’ g. Heterogeneity, risk of publication bias, quality of studies/interventions, and researcher allegiance, were evaluated. Meditation techniques incorporated attentional elements, and five of them also added constructive practices. No studies were found using deconstructive exercises. The overall ES was g = −0.23 [95% confidence interval (CI) −0.40 to −0.07], favouring meditation (number needed to treat = 7.74). Heterogeneity was low (I2 = 2; 95% CI 0 to 56). There was no evidence of publication bias, but few studies and interventions were of high quality, and allegiance might be moderating results. Meditation seems to be a bit more effective than relaxation in the treatment of anxiety, and it might also remain more effective at 12-month follow-up. However, more research using the full spectrum of meditation practices to treat different anxiety disorders, including independent studies to avoid researcher allegiance, is needed if we are to have a precise idea of the potential of these techniques compared to relaxation therapy.