Are you talking romantic liking or just normal everyday liking? Being a step-cousin, there's no blood involved here - just a co-mingling of families. So my vote is yes, it's ok but don't blast this news all over the family. Continue to get to know your cousin in a platonic way. That way, if the cousin doesn't reciprocate your feelings, no harm done, and you guys can still be friends.
Like Danae said.
Also, just as an FYI, in most cultures it is expected that first cousins will become romantically involved at some point. This is because when kids first become interested in the opposite gender, the ones they have the most contact with are their cousins. The USA is "odd man out" on this issue, and not even all of the USA views such relations as "taboo".
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