Chronic toxicity of arsenic resulting from drinking water is a health problem encountered in humans, especially in South America and Asia, where a correlation between oxidative stress, tumor promotion, and arsenic exposure has been observed. Differential solvent extraction (petroleum ether (PE); dichloromethane (DCM); methanol (OL) and water (W)) was performed to compare the protective (antioxidant) activity of five Argentinian medicinal plants on arsenite-induced oxidative stress in Vero cells, assayed by hydroperoxide measurement. The results were analyzed using ANOVA followed by the LSD Fisher test. The data showed that arsenite was a pro-oxidant agent which acts in a time–dose-dependent manner. Extracts from Eupatorium buniifolium (PE), Lantana grisebachii (PE, W), Mandevilla pentlandiana (PE, W), and Sebastiania commersoniana (DCM, OL, W) prevented the formation of both aqueous and lipid hydroperoxides, but Heterothalamus alienus only impeded lipid ones. Therefore, antioxidant extracts are potentially beneficial and may have a protective activity against arsenite-induced renal injury. Among these, the aqueous extract of L. grisebachii may represent the most suitable preparation for humans since the traditional usage of this plant in popular medicine is through consumption of tea.