Static and dynamic light scattering measurements on polystyrene/poly(methyl methacrylate)/bromobenzene solutions under the optical theta condition are reported. The theta condition is fulfilled by knowing that the average increment of refractive index of the two polymers is zero and letting their composition be 1/2. The total polymer concentration is kept constant and the temperature is changed from 30 degrees C to the critical temperature T-c which is found at 2 degrees C. The results reveal two distinct ranges of temperatures where both static and dynamic properties show different behaviors. The upper range of temperatures which is above 7 degrees C in this mixture can be described quite well with the mean field model based on the random phase approximation. In particular the dynamic scattering function relaxes with a single exponential whose decay rate fits well to the theoretical prediction using the above approximation. Below 7 degrees C, the results show strong effects of the critical fluctuations which manifest themselves in the static properties by critical exponents of the Ising type. The dynamic correlation function decays by following a bimodal distribution and the slow mode decays according to the critical slowing down, as predicted by the mode coupling theory. The first cumulant of the dynamic scattering function is analyzed as a function of the temperature, and good agreement is found with the theoretical framework based on the mode coupling model and using the measured structure factor. From the intermediate q region where the first cumulant has a q(3) behavior, the viscosity of the mixture is deduced and analyzed as a function of temperature.