First, the seal of Solomon is traditionally imagined as either a pentagram or a hexagram, so if you are talking about the pentagram and not the star of david, then the history is a little different but only just. As far as I can tell from researching, it seems that the idea that there was anything magical about a pentagram comes from medieval Christendom as a symbol of various things that came in fives (five senses, five elements, five wounds of Christ). Medieval arabic tradition imagined that the symbol (more often a hexagram than a pentagram) was inscribed on a magic ring that the possessor could use to command deamons/djinni or or perform other magical feats. It doesn't seem like either the symbol or its magic was specifically thought to be evil as King Solomon is characterized as good and wise.

The popularity of the pentagram as a magical symbol continued through western occultism.

The idea that the inverted pentagram (two points level at the top) is a symbol of evil/the devil/demons etc. seems to have been a thoroughly modern innovation by 19th century occultists like Eliphas Levi. Christians who concerned themselves with the idea of God's opposing force picked it up from them. Obviously in reality there is no basis for any claim that it has any actual magical or spiritual significance. It was just a symbol of things that come in fives (naturally or unnaturally).