England number one Hart has spent the last four Manchester City matches on the bench following a handful of errors for club and country.
However, Seaman, who spent the 2003-04 campaign with City, believes that Pellegrini should have stuck with Hart, just as England boss Roy Hodgson has done.
"Hart is brilliant. I was surprised he was dropped by City. He's a quality goalkeeper and is playing big pressure games every week and you can't say that about the other goalkeepers," he told talkSPORT.
"He's by far our best keeper and I was glad Roy Hodgson came out and backed him. That's what you want as a goalkeeper. It's a shame his own [club] manager hasn't backed him as well."
Seaman made 26 appearances during his stint with the Citizens.