An atom consists of three kinds of particles: electrons, protons and neutrons. Now the neutrons do not have any electrical charge on them and are therefore electrically neutral.
Protons have a positive charge that is usually expressed as +1 though in terms of coulombs it is + 1.602*10^-19. The electron has a negative charge that is expressed as -1 and in terms of coulombs is equal to -1.602*10^-19.
A neutral atom has the same number of electrons as the number of protons in it. Therefore the net charge in an atom is equal to zero. This makes an atom electrically neutral.
Because a balanced atom usually has the same number of protons and electrons, and since it is the electrons that determine the negative charge of the atom, and the protons that determine the positive charge of the atom, the two charges cancel each other out.