Background: Mindfulness-based interventions (MBIs) and cognitive behavioral therapy (CBT) have both been shown to be effective treatment approaches for anxiety. The purpose of this paper was to directly investigate the ability of MBIs and CBT to improve anxiety symptoms (primary outcome), as well as depression symptoms and sleep quality (second outcome). Methods: We searched the following electronic databases from 1st December, 2019 to 14th January 2021: English databases including PubMed, PsycINFO, Web of Science, the Cochrane Library, Elsevier, Springer Link, Wiley Online Library, ClinicalTrails, and Embase, and Chinese database including CNKI, WANFANG, and CQVIP. The eligibility criteria included the following: (I) patients with anxiety disorders or symptoms of anxiety; and those with physical or mental disorders with comorbid anxiety symptoms; (II) randomized controlled trial (RCT) design; (III) the treatment group received MBIs; (IV) the control group received CBT; and (V) the treatment outcomes were anxiety, depression, and sleep quality. Results: In total, 4,095 abstracts were reviewed. Of these, the full-texts of 45 articles were read in detail; and 11 RCTs were finally included in the analysis. Upon completion of MBIs and CBT group sessions, the study outcomes (mean anxiety, depression, and sleep quality scores) revealed no difference between MBIs and CBT with regards to anxiety, depression, and sleep quality post-intervention. Subgroup analysis was also performed, and the results indicated that MBIs may provide a small advantage for people with anxiety symptoms compared to CBT [standard mean difference (SMD): –0.36, 95% confidence interval (CI): –0.66 to –0.06], while the CBT group demonstrated a small comparative advantage for anxiety in the Liebowitz Social Anxiety Scale (LSAS) and Social Phobia Inventory (SPIN) scales, as well as mindfulness-based stress reduction (MBSR) in the types of MBIs (LSAS: SMD: 0.35, 95% CI: 0.08 to 0.63; SPIN: SMD: 0.51, 95% CI: 0.11 to 0.92; MBSR: SMD: 0.41, 95% CI: 0.07 to 0.74). Discussion: There was no significant difference between MBIs and CBT in terms of the treatment outcomes of anxiety, depression, and sleep quality. MBIs could be used as an alternative intervention to CBT for anxiety symptoms. Trial registration: This meta-analysis was conducted in line with the PRISMA guideline and was registered at PROSPERO https://www.crd.york.ac.uk/PROSPERO/ (CRD42021219822).