Oxford scored two goals in one game for the first time since Boxing Day to ease their relegation fears.
Congolese striker T'Cham N'Toya opened the scoring after just 41 seconds as Barnet keeper Ross Flitney miscued a clearance straight to the forward.
And he struck again in the 25th minute as he controlled Chris Hargreaves's header before calmly firing home.
Barnet improved after the break but only had a Paul Warhurst drive to show for their efforts.
Oxford Utd: Turley, Quinn, Willmott, Roget, Robinson, Mansell, Hargreaves, Smith (Brooks 82), Sabin (Sills 90), Basham (Burgess 61), N'Toya.
Subs Not Used: Guatelli, Dempster.
Booked: Smith.
Goals: N'Toya 1, 25.
Barnet: Flitney, Hendon (Batt 65), Warhurst, Charles, Clist, Fuller, Bailey, Hessenthaler (Sinclair 68), Vernazza, Kandol, Strevens (Hatch 64).
Subs Not Used: Reed, King.
Att: 6,948
Ref: G Hegley (Hertfordshire).