Justice Wadyajena was accused of using “abusive language” against a fellow Zanu-PF party member, who had a portrait of Mrs Mugabe on his car.
The incident is being seen as part of internal party wrangling over who should succeed President Robert Mugabe.
Two camps have emerged, one backing Mrs Mugabe and the other the 91-year-old leader’s deputy Emmerson Mnangagwa.
Mr Wadyajena is reported to be loyal to Vice-President Mnangagwa while the man he argued with, Jimayi Muduvuri, supports Mrs Mugabe.
Both men were attending the party’s recent conference in the resort town of Victoria Falls.
On Friday, Mr Mugabe told the party conference that such factionalism within Zanu-PF was destructive and warned the country’s security forces to stay away from politics.
But the BBC’s Brian Hungwe in the capital, Harare, says the infighting appears to be worsening.
Mr Wadyajena was quoted in court papers as having told Mr Muduvuri: “You are a fool, as well as that ‘mother’ of yours.”
The first lady is referred to as “amai”, meaning mother, by supporters of Zanu-PF.
The MP, who represents Borrowdale Brooke in Harare, was granted $800 (£500) bail and is expected to go on trial on 5 January.
Mrs Mugabe held rallies across the country ahead of Zanu-PF’s conference, which many have seen as a sign of her political ambitions.
The 50-year-old first lady took over the ruling party’s women’s league last year after spearheading the expulsion of former Vice-President Joice Mujuru and her supporters from Zanu-PF.
Mr Mnangagwa, 69, is a veteran of the independence struggle and Zanu-PF and also served as the country’s spymaster in the 1980s.