yes
the oxford dictionary defines porn like this: pornography /pɔːˈnɒɡrəfi/: printed or visual material containing the explicit description or display of sexual organs or activity, intended to stimulate sexual excitement.
so by that definition, yes. however, some sources (e.g. psychology today) define porn's SOLE purpose to be sexual stimulation. yaoi nowadays usually doesn't just want to arouse someone. there are plenty of yaoi works that have really great and interesting plot. so if you read yaoi just for the sex scenes then yes, it's porn, however if you really do enjoy its plot, i'd consider it more to be erotica.
Is yaoi considered p*rn??