Do any characters from the main series of "Attack on Titan" appear in "Before the Fall"? I just started reading Attack on Titan: Before the Fall and just had an urge to know whether there is any known face in the series with our current main series.

Does anyone appear in Before the Fall?
No, there is none. 

Before the Fall is set decades before the main Attack on Titan series. Even if some of the older characters in the main series were already born during this time, they were not deemed significant enough to be depicted in the story yet since they made no appearances and the story is mainly focused on Kuklo and his time with the Survey Corps.