In this study, the regularity of neuronal firing is investigated. We perform independent simulations to find out effects of synaptic transmission reliability in the background activity on the firing regularity of neurons, using Integrate and Fire (IF) neuron model. The obtained results demonstrate that synaptic transmission reliability changes firing regularity influencing background activity intensity. Moreover, it is investigated how the excitatory and inhibitory synaptic connections effect the regularity of neuronal firing.