Van Dijk was speaking after Burnley held Liverpool to a 1-1 draw at Anfield on Saturday.
"Frustration is the word which is definitely in my head," said Van Dijk.
"After 60 minutes, we started to become sloppy and it's not the first time. We have to address that. It's been spoken about already but we have to address it again apparently.
"We have another 48 hours to assess it, ourselves and the staff, and we will debrief and then we have to act.
"I'd say there is something lacking at the moment and we want to change that."
Liverpool will hope for an improved cutting edge when Mohamed Salah returns this week from Egypt's Africa Cup of Nations campaign.
"Everyone should look forward to that," said Van Dijk. "With his quality he can win games and have good results.
"Mo is a very important member of our squad on and off the pitch. Unfortunately he couldn't get to the final of the Afcon but when he is back he needs to help us."