There are several candidates for titles which may have been applied to Nero by the early church, among them of course, "the antichrist" (1 John), "the beast" (Rev. 13), and "the man of sin" (2 Thes. 2). The relationship between those titles is a fascinating study.

Given the context of the times, with all the persecution, I would tend to concur with Jeopardy that "the antichrist" would be the most likely title that may have been applied to Nero by the early church. That is not to say that I think Nero was, in fact, the antichrist, or indeed that that title necessarily refers to a specific individual.

While Nero may have been referred to as "the beast" by his lieutenants, and while that may be a suitable appellation, given the late date of the writing of the book of Revelation, I doubt that it would have been in sufficiently wide circulation at the time, in order for that title to be commonly used by the early church.

Just my two cents.

Meta4

There is no such thing as preaching Christ and Him crucified, unless we preach what nowadays is called Calvinism. It is a nickname to call it Calvinism; Calvinism is the gospel, and nothing else. - C.H. Spurgeon