Based on a solution of the Floquet Hamiltonian we have studied the time evolution of electronic states in graphene nanoribbons driven out of equilibrium by time-dependent electromagnetic fields in different regimes of intensity, polarization, and frequency. We show that the time-dependent band structure contains many unconventional features that are not captured by considering the Floquet eigenvalues alone. By analyzing the evolution in time of the state population we have identified regimes for the emergence of time-dependent edge states responsible for charge oscillations across the ribbon.If a time-periodic field is applied to electrons in a periodic lattice the Bloch theorem can be applied twice, both in space and in time. This is the essence of Floquet-Bloch theory [1][2][3] that has recently attracted a renewed interest for its ability to describe topological phases in driven quantum systems [4][5][6][7]. The discovery that circularly polarized light may induce nontrivial topological behaviour in materials that would be standard in static conditions [8][9][10][11] has opened the way to the realization of the so-called Floquet topological insulators, where a topological phase may be engineered and manipulated by tunable controls such as polarization, periodicity, and amplitude of the external perturbation.When the field is applied for a sufficiently long time (pulse duration much larger than the field oscillation period) electrons reach a nonequilibrium steady state characterized by a periodic time-dependence of the wave functions and, consequently, of the expectation values of any observable [12,13]. In this paper we focus on this time-dependence, looking for the time evolution of some relevant quantities such as energy and charge density. How these characteristics affect the time behaviour of these observables will be our focus. We will consider the prototypical case of graphene that under the influence of circularly polarized light exhibits in its Floquet band structure the distinctive characteristics of a 2D Chern insulator, namely, a gap in 2D and linear dispersive edge states in 1D [9,11,14,15]. These Floquet edge states are topologically protected and responsible for a quantized Hall conductance in the absence of a magnetic field [16][17][18], a remarkable realization of the so-called "quantum Hall systems without Landau levels" originally proposed by Haldane [19].Under a periodic drive, the nonequilibrium steady states, solutions of the time-dependent Schrödinger equationevolve in time aswhere 훼k (r, ) is periodic in time and 훼 (k), the Floquet quasi-energies, are the eigenvalues of an effective Hamiltonian̂퐹 ≡̂− ( / ), the so-called Floquet Hamiltonian:퐹 훼k (r, ) = 훼 (k) 훼k (r, ) .Herê(r, ) is the full Hamiltonian of the driven system (r, ) =̂0 (r) +̂(r, )