The use of plants and their products as sources of antioxidants to enhance health and food preservation is currently of great interest. Many plant species, especially those belonging to the Lamiaceae family have exhibited strong antioxidant activity. Salvia macrosiphon is an endemic medicinal plant in Iran, belonging to Lamiaceae family and has many pharmaceutical properties. This study was carried to evaluate the effects of different concentrations of sodium chloride [0.4 (control), 2.3, 4.5 and 6.8 dSm−1] on growth, total phenolic content and antioxidant activity of S. macrosiphon plants. Results showed that salinity stress affects plant growth by changing plants’ both fresh and dry weights. In addition, although total phenolic content in S. macrosiphon plants decreased with salinity, there was an increase in leaf antioxidant content. The absence of correlation between phenolic contents present in S. macrosiphon plants and antioxidant activity could be explained by the fact that other antioxidant molecules are also synthesized under stress conditions.