If you are speaking of real tea, meaning it came from the camilla sinensis plant, there will always be some level of caffeine in the tea. Even in tea marked as decaffinated, a very low level of caffeine will still exist.
However, many people commonly make the mistake of calling an herbal tisane, herbal tea. The truth is that there is no such thing as a "herbal tea" because in order to be classified as "tea" the beverage must be brewed from the leaves of camilla sinensis, which an "herbal tea" lacks.
The point being that any "tea" containing camilla sinensis will contain caffeine. But if you purchase an herbal tisane or "herbal tea" as so many incorrectly call it. It will not contain caffeine.