Herbal extracts have various biological properties, including antioxidant activity (AAC). This activity is mainly associated with presence of polyphenolic compounds, and depends on the type and origin of the raw material, the chemical profile, and the extraction method (including the type of solvent used). The aim of the study was to evaluate the chemical compound content and antioxidant activity in selected plants from the Lamiaceae family, depending on the solvent applied. Additionally, the study aimed to determine whether there are correlations between the content of biological compounds and antioxidant activity. The extracts were prepared from Thymus vulgaris L. and Sideritis scardica Griseb. using ethanol, methanol, ethyl acetate, and acetone as solvents. The obtained extracts were assessed for total polyphenols content (TPC), flavonoids, and phenolic acids, as well as antioxidant potential, using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and ferric reducing (FRAP) assays. The plants studied showed significant TPC and significant AAC, with the sideritis extracts exhibiting both high TPC (162.38 mg GA/g) and high AAC-DPPH (86.39%). Our study showed a significant positive correlation between antioxidant activity (DPPH) and antioxidant activity (FRAP) for acetone extracts (r = 0.664808), and strong negative correlations for the other extracts. It was also confirmed that selecting the appropriate solvent is essential for the efficient extraction of phenolic compounds, which are strongly linked to biological activity. As a result, extracts of T. vulgaris and S. scardica represent a potential source of antioxidants that could be used in the prevention of various diseases or in the food industry as preservatives.