Lomas was handed the punishment after being sent to the stand during St Johnstone's 1-1 draw against Celtic last month.
A statement on the Perth club's official website read: "The SFA have this afternoon handed Steve Lomas an eight-match touchline suspension following his dismissal from the dugout in the match against Celtic on 11th November for foul and abusive language towards a match official."
The club added: "This ban consists of six games for the offence committed at Celtic Park plus the suspended two-game ban which was already hanging over him following the game against Ross County in Dingwall in September."
Lomas was also sent to the stand towards the end of his side's 1-0 defeat by Hibernian last night, for which he could face additional sanction.
It is another blow for the club, who lost midfielder David Robertson to a broken leg in the same match.