A candidate who is listed on the general election ballot as a Libertarian is considered:

Answer: A minor party candidate

Explanation:

Libertarians are usually those people who opposes the ruling of the government because they believe people doesn't need to be ruled by their government, the government need to only intervene in critical matters but must not interfere in a life of individual. Therefore they are likely to be only a minor party.

A minor party is a political party that doesn't have a significant role when compared to a major party. Minor party have little to no role in the political ruling. However they can always have that one seat or a candidate who represent their ideas.