Pure peppermint tea made of nothing but the peppermint plant is 100% caffeine-free. Similarly, all other plants in the mint family, including spearmint and many other herbs, are also caffeine-free.

However, sometimes peppermint or other mints can be blended with green or black tea, or other teas from the tea plant, Camellia sinensis, or with other caffeine-containing plants like Yerba mate. These blends can contain caffeine. Typically "Moroccan mint tea" is a blend of mint and green tea.

When buying mint tea, if you desire a caffeine-free herbal tea, check the ingredient list, and/or check for the term caffeine free on the label. "Herbal tea" usually implies, but does not guarantee that a blend is caffeine free--because Yerba mate and a few other plants are considered "herbal teas" but contain caffeine.