Medicinal plants are one of the sources of biologically active compounds that determine their therapeutic effect. Water infusions and decoctions, as well as tinctures and extracts, are currently used in phytotherapy. Sonication treatment is an effective approach to increasing the efficiency of active component extraction from plant material. Application of sonication reduces the time and consumption of extractant, as well as uses mild conditions. Sonication-assisted water extraction was applied to the various medicinal plants traditionally used in phytotherapy. Water extracts from herbs, leaves, bark, infructescences, flowers, roots, and rhizomes were studied using total antioxidant parameters obtained by constant-current coulometry. Eleven samples of commercially available medicinal plants were investigated (bark of Quercus robur and Frangula alnus, infructescences of Alnus incana, rhizomes of Potentilla erecta and Bergenia crassifolia, roots and rhizomes of Sanguisorba officinalis, herb of Leonurus, flowers of Tilia×europaea and Matricaria chamomilla, leaves of Salvia officinalis and Urtica dioica). Total antioxidant capacity (TAC) and ferric reducing power (FRP) based on the reactions with electrogenerated bromine and ferrocyanide ions, respectively, were evaluated. The effect of sonication time in the range of 10–30 min was tested. The highest yield of antioxidants was achieved using a 30 min treatment. The TAC and FRP values were varied depending on the part and type of medicinal plant. The highest TAC and FRP were obtained for the extracts obtained from roots and rhisomes. The FRP values indicate the impact of phenolic compounds, which is significant for the samples under study. Total antioxidant parameters of infusions, decoctions, and sonication-assisted extracts were compared.