If a runner scores off of a balk, is it considered an earned or unearned run?

According to rule 10.18(a)

"An earned run shall be charged every time a runner reaches home base by the aid of safe hits, sacrifice bunts, a sacrifice fly, stolen bases, putouts, fielder's choices, bases on balls, hit batters, balks or wild pitches (including a wild pitch on third strike which permits a batter to reach first base) before fielding chances have been offered to put out the offensive team. For the purpose of this rule, a defensive interference penalty shall be construed as a fielding chance."

So a balk would result in an earned run. There is one way it could be unearned with no errors earlier in the inning and that would be if the runner moved up a base because of a passed ball or reached base on a strikeout/passed ball.

Basically, an earned run is a run that is caused by the pitcher. Whether he gives up a hit, home run, commits an error, or a balk. As long as the pitcher caused it, its an earned run. In this case the balk caused the earned run. Im assuming that your watching the Cleveland-Texas game, which is what sparked your curiosity. Hope this helped.

it depends on how he got on base, if it was a hit then its and earned run if he reached first on on an error its unearned

Rule 10.18(a)(1)

A wild pitch is solely the pitcher's fault, and contributes to an earned run just as a base on balls or a balk.

http://www.baseball-almanac.com/rule10.shtml

It was the pitcher's fault. It is an earned run.