Tigers players surrounded referee Mark Clattenburg after Arsenal full-back Kieran Gibbs was only booked for fouling Lazar Markovic when the Hull winger was clear on goal.
That resulted in a Football Association misconduct charge, which the club have admitted.
"Hull City have been fined Â£20,000 after admitting an FA misconduct charge and accepting the standard penalty," said a statement from the FA.
"In the 55th minute of the game against Arsenal on February 11 2017, the club failed to ensure that its players conducted themselves in an orderly fashion, contrary to FA Rule E20 (a)."
Source : PA