United lost 2-0 on the day with goals coming from Virgil van Dijk and Mohamed Salah at Anfield.
The incident that necessitated the fine occurred in the 26th minute when the visiting players surrounded referee Craig Pawson for initially allowing Roberto Firmino’s goal to stand following a challenge on goalkeeper David De Gea by Van Dijk.
De Gea led the protests and was joined in by the likes of skipper Harry Maguire, Luke Shaw, Andreas Perreira and Fred.
The goal was however chalked off following a Video Assistant Referee (VAR) review but De Gea was cautioned for his involvement in the incident.
"Manchester United FC has been fined £20,000 after admitting a breach of FA Rule E20 and accepting the standard penalty," Friday’s statement from the FA read.
"The club failed to ensure its players conducted themselves in an orderly fashion during the 26th minute of a Premier League fixture against Liverpool FC on 19 January 2020."
The Red Devils remain fifth on the league log, six points behind fourth placed Chelsea, after losing 2-0 at home to Burnley on Wednesday.
Ole Gunnar Solskjaer’s men return to action on Sunday with an FA Cup fourth round trip to League One side Tranmere Rovers.
