With just four wins in their previous 14 games in all competitions, Alan Pardew's men have seen their season peter out, sitting comfortably in mid-table, well away from both the relegation zone and the European qualification places.
However, the Magpies were booed by their own fans after a woeful showing in last weekend's 4-0 defeat at Southampton, and Santon understands their frustrations.
"Against Southampton, our mentality was wrong," Santon told The Sun.
"We played like it was a friendly game.
"The fans were right - they booed and I wasn't surprised.
"They had come a long way, they spent a lot of money and I think they deserved better than what they saw."
Many have accused the Newcastle players of already being in holiday mode as they have very little to play for.
However, Santon insist that is not the case, and they will be doing their utmost to improve their final league position.
"The season might be nearly gone but we must always play in the same way," the Italy full-back added.
"The manager has told us we always need to have a winning mentality - whether it be a big or a small team."