According to the NY Post, she could be. Below is how they are reporting it...

Music insiders are chattering about Beyoncé expecting her second child with husband Jay-Z. Multiple sources told us after the Met Gala last week that the singer, who is currently in the middle of a world tour, is pregnant. Bey wore a Givenchy gown with a high, belted waist that carefully camouflaged her midsection, but pictures have emerged on blogs of what looks like a baby bump from recent tour dates.  (source: lindaikejiblog)