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Kagome magnets have been proposed to host many exotic phenomena, such as spin liquid and Weyl semimetal phases. A hallmark signature of their band structure is a dispersionless "flat" band, accopanied by a Dirac dispersion near the Brillouin zone edge. We use low-temperature spectroscopic-imaging scanning tunneling microscopy (SI-STM) to investigate the surface structure and low energy electronic properties of a kagome magnet YMn₆Sn₆. We find a sharp spectral peak E_p close to the Fermi level, which can be linearly tunned by magnetic field closer to Fermi level. By further imaging scattering and interference of electrons on the kagome Mn surface, we are also able to visualize a Dirac like band dispersion, terminating near E_p. Remarkably, external magnetic field also shifts this Dirac dispersion to higher energy regardless of the relative direction of the magnetic field. This diamagnetic behavior cannot be explained by spin Zeeman coupling, and points towards the emergence of orbital magnetism in this system.