Murphy has kept 15 clean sheets this season, but does not feel he has been in his best form.
"I'm pleased, but a little bit embarrassed to be honest. Whether I deserve it or not, I don't know," he told the Scunthorpe Telegraph.
"It's always nice to get individual awards, especially from your fellow professionals, people you have played against.
"They can't have seen a couple of the goals where I thought I could have done better. I always look back at the game to see if I could have done better. This year I think I could have done better a lot more."
The PFA awards are voted for by players, and the organisation's chief executive Gordon Taylor has had to defend the system after criticism of Ryan Giggs' award as the Premier League's player of the year.
The veteran Welsh winger has started only 12 games for Manchester United this season, prompting suggestions the vote was based on sentiment rather than performances.
"Sometimes you can make a big impact in relatively few games and he's still capable of showing his skill at his age now as when he was nominated 15 years ago," he told BBC Radio Five Live.
"There may well be [a change in the timing of the vote] but it has its own slot now and in general, for the vast majority, the players have been spot on.
"You could have one match of Ryan Giggs which could be worth 40 of another player, so sometimes you don't just drink the best wine in the world every night of the week but it can have a long-lasting effect."