The aim of the present study was to evaluate the antioxidant activity of essential oil and extracts obtained from the aerial parts of celery (Apium graveolens L.) and from flaxseeds (Linum usitatissimum (Linn.)). In vitro antioxidant activity was determined by 2,2-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing power assay. Results showed that the essential oil of celery and methanol extracts of celery and flaxseeds exhibited a good scavenging activity of DPPH radical respectively 84 ± 0.4%, 79 ± 0.5%, and 78 ± 0.3% at concentration of 1000 µg mL^-1 comapred to the queous extracts. These results were lower than those found with ascorbic acid 96.23 ± 1.2% and catechin 94.50 ± 1.4% at the same concentration. IC50 is defined as concentration of substrate that inhibits 50% of the DPPH radicals present in the reaction medium. The positive control catechin and ascorbic acid displayed lower values of IC50 (7.81 ± 0.1, 31.5 ± 0.3 µg mL^-1), followed by methanol extract of celery and flaxseeds (130 ± 0.2, 150 ± 0.4 µg mL^-1), essential oil of celery (180 ± 0.2 µg mL^-1), then aqueous extracts of flaxseeds and celery (950 ± 0.5, 980 ± 0.4 µg mL^-1). For aerial part of celery, ​​significant activities for reducing iron were obtained, values ​​observed by optical density (OD) of 1.8 ± 0.2 for essential oil and 1.7 ± 0.1 for methanol extract, while ascorbic acid and catechin provided an OD of 2.069 ± 0.03 and 2.66 ± 0.016 in the same concentration 1000 µg mL^-1. The results of the current study showed that flaxseeds and celery exhibited a higher antioxidant activities that could be exploited in food and pharmaceutical industries.