The hosts appeared to be heading for a first win in three matches when Miller fired home from the penalty spot in the 16th minute after he was tripped in the area.
But Maidstone levelled on the hour mark through Jamar Loza, whose cross caught out goalkeeper Steve Arnold and flew in off a post.
Dover almost stole the points late on but Miller's shot was well saved by Lee Worgan.
Report supplied by the Press Association.
Match ends, Dover Athletic 1, Maidstone United 1.
Second Half ends, Dover Athletic 1, Maidstone United 1.
Substitution, Maidstone United. Joseph N'Guessan replaces Yemi Odubade.
Substitution, Maidstone United. Bobby-Joe Taylor replaces Vas Karagiannis.
Substitution, Dover Athletic. Sammy Moore replaces Moses Emmanuel.
Substitution, Dover Athletic. Jim Stevenson replaces Jack Parkinson.
Goal!  Dover Athletic 1, Maidstone United 1. Jamar Loza (Maidstone United).
Second Half begins Dover Athletic 1, Maidstone United 0.
First Half ends, Dover Athletic 1, Maidstone United 0.
Ricky Modeste (Dover Athletic) is shown the yellow card for a bad foul.
Alex Flisher (Maidstone United) is shown the yellow card for a bad foul.
Goal!  Dover Athletic 1, Maidstone United 0. Ricky Miller (Dover Athletic) converts the penalty with a.
Lee Worgan (Maidstone United) is shown the yellow card for a bad foul.
Tom Mills (Maidstone United) is shown the yellow card for a bad foul.
First Half begins.
Lineups are announced and players are warming up.
Ricky Miller netted his 25th goal of the season but Dover spurned the opportunity to move into the National League play-off positions following a 1-1 home draw with Maidstone.