Mansfield were left to rue missed chances as Ismail Yakubu and Adam Gross helped Barnet to a much-needed win.
Barnet snatched the lead against the run of play in first-half injury-time with Jason Puncheon's corner headed home by Yakubu.
They then doubled their advantage after the break when Gross finished from eight yards out.
Richie Barker grabbed an 84th minute consolation goal for Mansfield, heading in Matt Hamshaw's free-kick.
Barnet: Harrison, Hendon, King, Yakubu, Gross, Bailey, Sinclair, Puncheon, Graham, Warhurst, Vieira (Cogan 79).
Subs Not Used: Flitney, Charles, Devera, Nicolau.
Goals: Yakubu 45, Gross 54.
Mansfield: White, Mullins, Baptiste, Hjelde, Jelleyman, Brown, Coke (Lloyd 83), D'Laryea, Hamshaw, Barker, Beardsley (Reet 65).
Subs Not Used: Muggleton, Arnold, Charlton.
Goals: Barker 84.
Ref: S Bratt (West Midlands).