Two first-half goals gave the Partenopei a 2-0 lead just before half-time, but they squandered the lead with a late goal from Dusan Basta securing a point for the visitors.
The former Liverpool boss admits that he is unhappy that the club's fortunes have turned upside down following a bright start to the season.
"We made two mistakes from set plays, including an own goal, and we are suffering because we make mistakes we should not be making," Benitez told Sky Sport Italia.
"This result means we still have to improve, as I’ve said many times. We should be in control of a match and then we make a mistake. We are the ones who make the errors and we have to do better.
"Of course we all expect Napoli to be at the level they were at early in the season and for the side to have more points by now. We cannot be satisfied with this and I am the first to be unhappy."
Benitez then went on to discuss Napoli's must win clash against Arsenal on Wednesday, believing that his experience working in the "toughest league" will assist his troops in prevailing over their English rivals.
"Clearly it’s a different competition and if we score goals the way we did today, then we have to do better when defending," the Spaniard added. "Those two errors on the set plays really should not be happening and they changed everything.
"The way to beat Arsenal is to keep a tight team, have intensity, move the ball around and close the spaces. Having worked in La Liga and the Premier League, I think Serie A is the toughest league."
The draw leaves Napoli eight points adrift of league leaders Juventus and they currently sit in third position.