While critics disagree about Frost's place as a modernist poet (many argue that he is a pastoral poet... one concerned more with the sensuality of nature than the angst of the modern man) several of his poems are rife with modernist themes, particularly loneliness, isolation, and frustration.
Of the three you list here, "Acquainted with the Night" offers perhaps the most overt modernist approach. The speaker's sense of being alone in, if not an outright hostile world, is certainly not a world that is an ally to the individual. The speaker walks in the darkness "in rain -- and out of rain." In a brief encounter with the night watchman, he shuns human interaction. He hears footsteps and stops; he hears a cry and does not respond or investigate. All of these combine to give a sense of the modernist sense of being both distanced from others and isolated within the self.
"Mending Wall" shares the modernist themes of separate-but-together. "Something there is that doesn't love a wall," the poem begins, "That sends the frozen-ground-swell under it, / And spills the upper boulders in the sun; / And makes gaps even two can pass abreast." Modern man wants to make boundaries, but nature seems bent on throwing men together, making him fight again and again to maintain his foolish sense of privacy. The famous line "Good fences make good neighbors" comes from this poem, but there is no such thing as a stable fence or a good neighbor.
"The Oven Bird" is Frost's rather tongue-in-cheek take on those earlier, Romantic poets whose "birdsong," their poems, were active only in sunny, happy, pastoral conditions. Says critic George Montiero, "Unlike those poets who can burst into song only in the spring, [Frost] has learned the ovenbird's paradoxical trick. He has learned how to sing an unlyrical song in those times that are not at all conducive to joyous song." Modern times, for Frost, for many modernist writers, were hardly conducive to joyous times.