Anything that sparks your interest or makes you wonder has the ability to fascinate. If you catch someone's interest, and then hold it, you fascinate them. Be careful.
The word fascinate actually comes from Latin and French words meaning "witchcraft," and although these days fascinate is used under much tamer circumstances, there is some sense in the word that the person's appeal is not quite normal: there might be a spell-like quality to his or her charms. Thus, the word is often used to describe a new love. On the other hand, you might find the study of exotic beetles fascinating. To each his own.