Introduction Searching for plants with potential antioxidant activity has been increasing, particularly recently. Priorities have focused on plants which contain higher percentages of flavonoids, phenols and tannins. This study aimed to screen the phytoconstituents; total phenols, flavonoids and tannins of the aerial parts of Trigonella arabica and Trigonella berythea and to evaluate antioxidant activity of methanolic, acetone, aqueous and n-hexane extracts of both plants which are grown widely in Palestine. Methods Phytochemical screening was performed on aqueous, acetone, methanolic, n-hexane extracts for total flavonoids, phenols, tannins, proteins, carbohydrates, saponins, glycosides, alkaloids, steroids, and terpenoids contents using standard methods. The antioxidant activities were evaluated using the 2,2-diphenyl-1-picryl-hydrazyl-hydrate assay. Results Our results showed that T. arabica and T. berythea extracts contained saponins, alkaloids, proteins, carbohydrates, phenols, steroids, tannins and flavonoids. Quantities of flavonoids, phenols and tannins were higher in the extracts of T. arabica compared to those of T. berythea (93.97 ± 1.2 vs. 76.67 ± 1.1 mg RU/g), (85.34 ± 0.62 vs. 64.44 ± 1.44 mg GA/g) and (12 ± 0.76 vs. 9 ± 0.47 mg TA/g), respectively. Extracts of T. berythea showed higher antioxidant activities compared to those of T. arabica. The highest antioxidant activity was shown in the n-hexane extract of T. berythea as compared to a standard antioxidant (IC50 = 3.23 ± 0.84 μg/mL vs 2.9 ± 0.24 μg/mL). Conclusion Extracts of T. berythea grown widely in Palestine show higher antioxidant activities than those of T. arabica. Using aerial parts of this plant might be useful in promoting health. Extracts from this plant might have potential applications in pharmaceutical and cosmeceutical formulations in the future.