Borage seed oil (BSO) is one of the richest sources of ??-linolenic acid and linoleic acid, which are considered to retain plenty of health promoting benefits. However, its application in functional foods and dietary supplements remains limited owing to its superior vulnerability to oxidation. To solve this problem, ultrasound-assisted BSO-loaded nanoemulsions were prepared with modified starch incorporating different concentrations of peppermint oil (PO), as a natural antioxidant. The influence of different PO levels on the mean droplet size, rheology attributes, and oxidative stability of nanoemulsions stored at various temperatures (4, 25, and 40 °C) during 30 days storage was analyzed. In addition, DPPH and ABTS assays were used to determine the antioxidant activity and antioxidant capacity of BSO-loaded nanoemulsions, respectively. The optimized formulation (NE3; 5:5% v/v PO: BSO) exhibited a slight change in droplet size and oxidative stability at all temperatures during storage compared to other formulations. At a concentration of 328.08 μL/mL, formulation NE3 presented the minimum DPPH IC₅₀ at 40 °C, which was lower than other formulations. The findings of this study revealed that the maximum retained antioxidant capacity (99.42 μg Trolox/mL) was related to NE3 comprising (5:5% v/v PO: BSO) stored at 40 °C for 30 days; which could be accredited to the role of PO as a natural antioxidant in order to improve the oxidative stability of nanoemulsion delivery system. Taken together, co-encapsulation of BSO and PO within nanoemulsions provides novel insights regarding the development of functional foods, dietary supplements and beverages.