The Italian club defeated the Blaugrana 2-0 in the first leg at the San Siro last month.
"The competition still has the big guns and it is nice to be in it," ESPNSoccernet quotes Beckham as saying.
"People are talking about a shift in power with Barcelona having lost their first game [2-0 against Milan], but no one should ever doubt their players even now.
"They have a home game to come and it doesn't matter if they're two or three down. I know what it's like to play against them when they're up against it and it's not easy."
PSG will head into their second-leg clash against Valencia 2-1 up from the first leg played in Spain in February.