Phytonutrients (e.g., phenolic compounds and flavonoids) are secondary plant metabolites that play an important role in the defense against pathogens and protection from oxidative injury because of their potential ability to neutralize reactive oxygen species. The present study aimed to determine the antioxidant contents, scavenging activity, and toxicity of aqueous extracts of common Omani plants. The total phenolic content (TPC), total flavonoid content (TFC), scavenging activity against hydrogen peroxide (HO), and brine shrimp lethality of the aqueous extracts of commonly used Omani ethnobotanical plants were evaluated. The samples exhibited a wide range of the investigated parameters. TPC ranged from 0.52 to 65.14 mg gallic acid equivalent/g dry solid, whereas TFC ranged from 0.07 to 37.14 mg catechin equivalent/g dry solid. Moreover, the scavenging activity ranged from 6.9% to 91.9%. Among 18 plant species that were examined, , , , , , and showed high values in almost all parameters. At exposure levels of 1 to 1,000 μg/mL, the lethality test using four plants with the highest TPC values and scavenging activity (, , , and ) revealed that they may be safe for consumption as food or medicine. In general, the study demonstrated that some Omani plant species may be potential sources of phenolic compounds and flavonoids. Thus, these plant species should be propagated to be used in the food and nutraceutical industries. Moreover, they can be consumed to combat chronic oxidative stress-mediated diseases.