Some tar-like materials occur naturally, but many tars are manufactured by heating wood, coal, or other organic matter. Natural does not mean harmless or suitable for every use.
Tar sits in an awkward place between natural material and manufactured material. Natural bitumen and asphalt can seep from the ground without human help, so people often call them natural tars. Wood tar, including pine tar, begins with a natural feedstock, but the tar itself is made by heating that material in a special way.
Coal tar is also based on an organic source, but it is an industrial by-product of coal processing. Calling it natural would be misleading in everyday language. It comes from ancient plant matter transformed into coal over geological time, then transformed again by industrial heating.
The more useful question is not whether tar is natural, but what kind of tar it is. Pine tar, birch tar, coal tar, bitumen, asphalt, and roofing mastics have different origins, uses, and safety profiles. A natural-looking dark finish may still smell strongly, stain permanently, or contain compounds that need careful handling.
Natural materials can be useful, beautiful, and historically important, but they are not automatically gentle. Tar should be identified by source and intended use before anyone treats it as a craft material, preservative, roofing product, or historical substance.