The atomic number of an atom is determined by the number of protons it has in its nucleus. In this case, the atom has 6 protons. Therefore, the atomic number is 6.
The number of neutrons and electrons does not affect the atomic number. While neutrons contribute to the atomic mass, and electrons balance the charge of the atom, the atomic number remains solely defined by the number of protons. So, for this atom with 6 protons (and consequently also 6 electrons since it’s neutral), the atomic number is 6.