The study was performed on Centaurea cyanus, Chamomilla recutita, Majorana hortensis, Ocimum basilicum, Plantago lanceolata, Sinapis alba, and Valeriana officinalis harvested in Lithuania, Poland, and Ukraine. Our aim was to determine the differences in selenium concentrations, total polyphenols, and the antioxidant activity in same-species samples from different regions. Another goal was to assess the correlations between these variables within the species. We found variations in most species, but not in all regions of harvesting. In four of the six species from Ukraine, we observed the highest concentration of Se. The selenium concentrations ranged from 15−182 µg/kg DW, and the greatest variation between the regions occurred in S. alba. The level of polyphenols was 5.52−53.25 mg TAE/100 g DW, and the largest differences between the sampling regions occurred in P. lanceolata and O. basilicum. ABTS radicals scavenging ability ranged from 5.20−59.79 μM AAE/100 g DW, while the FRAP potential was 13.56−409.14 μM FeE/100 g DW. The largest differences in antioxidant activity were found in O. basilicum and M. hortensis. Pearson’s correlation coefficients indicate that polyphenols may be responsible for antioxidant activity in Ch. recutita, O. basilicum, and V. officinalis, and selenium is responsible for antioxidant activity in M. hortensis. However, both polyphenols and selenium play a role in the antioxidant properties of C. cyanus and P. lanceolata. Also, selenium in C. cyanus and Ch. recutita may affect the level of total polyphenols. The examined species may supplement the human diet with exogenous antioxidants.