Vieira was shocked to hear Arsenal had blown a 4-0 lead to draw 4-4 against Alan Pardew's team on Saturday.
He told BBC Radio Five Live: "Like everybody else I was quite surprised.
"It does show that in football if you don't work hard until the last minute, if you don't have 100% commitment, anything can happen. Newcastle is still a difficult place to go to."
He added: "I think Arsenal is still a great side, a fantastic team to watch.
"The fans have been a bit disappointed in the last few years but they have to keep believing in themselves because they're still a good side."