Baccharis dracunculifolia or rosemary-of-field is the principal botanical source used by Africanized bees Apis mellifera L. to produce green propolis in Southeastern Brazil. The phenolic compounds present in the plant and green propolis have been reported to be responsible for biological activities such as antioxidant capacity. This study aimed to optimize the ultrasound-assisted extraction of antioxidants compounds from rosemary-of-field using a central composite rotatable design (CCRD), and compare results to green propolis extract. An experimental design was performed to obtain responses of total phenolic content and antioxidant capacity. The results allowed observing that the optimum condition for both Baccharis dracunculifolia floral bud and raw green propolis antioxidant extraction was obtained with 99% ethanol solution. In this condition, Total Phenolic Content (TPC), Ferric Reducing Antioxidant Power (FRAP), and 2,2-diphenyl-1-picryl-hydrazyl (DPPH) values were 612.14 mg GAE. g−1 sample, 534.39 µM ferrous sulfate g−1 sample, and 72.37 µmol TEAC. g−1 sample, respectively, for floral buds. These results have confirmed that optimization is a key step for effective and sustainable extraction processes to be feasible on an industrial scale. The proposed process can be easily adopted on a larger scale, as it uses very few inputs and presents straightforward steps, with the advantage of high efficiency in the extraction of phenolic compounds from the studied matrices compared to the results from the literature. The high concentration of antioxidants indicates that the products obtained can be considered as a sustainable bioactive source for food and cosmetic purposes.