Freemasonry is not a religious order, and therefore as long as a freemason believes they are a Christian, they are Christian for the purposes of this site. Freemasons can also be Jewish, Muslim, Deist, or of any other faith as long as they believe in a Supreme Being.
From the New Hampshire Grand Lodge website, although nearly every Lodge has a similar blurb (emphasis mine):
Is Freemasonry a Religion?
Categorically, not. Freemasonry is not a religion, although there is a religious aspect of every Freemason. Those who claim that it is a religion either do not understand our tenets, are confused as to what constitutes a religion, or have simply made an error of judgement without basis of fact. Freemasonry does require that a man profess a sincere belief in God, but not as to how he practices it, or what else he might believe spiritually. It does not take the place of religion, nor does it supplant the teachings of any religion. If anything, it reinforces those moral teachings of religions that form the basis of all good societies.
Finally, it is one of the ancient landmarks of Freemasonry that there is never any secular or political discussion in any legally constituted Lodge. So seriously do all regular Lodges take this principle, that the penalty for such discussion is severe and could result in expulsion.
Except for the requirement that they believe in God, nothing about masonic teachings is intended to supersede or override Christian teachings.
This is not without some controversy, as there have been allegations (particularly from the Roman Catholic Church) that because Freemasonry doesn't explicitly prefer one faith over another, it is incompatible with the true Catholic faith.
This is codified in 1738 by Pope Clement XII's papal bull, In eminenti apostolatus specula (emphasis mine):
Now it has come to Our ears, and common gossip has made clear, that certain Societies, Companies, Assemblies, Meetings, Congregations or Conventicles called in the popular tongue Liberi Muratori or Francs Massons or by other names according to the various languages, are spreading far and wide and daily growing in strength; and men of any Religion or sect, satisfied with the appearance of natural probity, are joined together, according to their laws and the statutes laid down for them, by a strict and unbreakable bond which obliges them, both by an oath upon the Holy Bible and by a host of grievous punishment, to an inviolable silence about all that they do in secret together.
Via this bull, the charge for joining a Masonic order is excommunication.
This was again reiterated in 1983 by the Congregation for the Doctrine of the Faith in its "Declaration on Masonic Associations:"
Therefore the Church’s negative judgment in regard to Masonic association remains unchanged since their principles have always been considered irreconcilable with the doctrine of the Church and therefore membership in them remains forbidden. The faithful who enrol [sic] in Masonic associations are in a state of grave sin and may not receive Holy Communion.
