  {\it Fermi} satellite has detected extra spectral components in GeV energy
range in several GRBs. Those components have power-law shapes, which may
contribute to also X-ray band. The limited photon statistics make it difficult
to determine the origin of GeV photons, namely internal or external shocks. We
try to explain the extra components with our numerical simulations based on
internal dissipation picture. Our leptonic model may reproduce not only the GeV
excess via SSC emission but also the low-energy excess via the late synchrotron
emission from remnant electrons. The hadronic models also reproduce keV-GeV
power-law components by synchrotron and SSC emissions from secondary
electron-positron pairs. In most cases the hadronic models require a much
larger energy of protons than gamma-rays. However, the keV-GeV flat spectra
detected in GRB 090902B is well explained with a comparable energy in protons
and gamma-rays Finally, we discuss both advantages and weaknesses for both the
leptonic and hadronic models. To overcome difficulties in internal dissipation
models, we propose introduction of continuous acceleration similar to the
second-order Fermi acceleration.
