  We investigate the external field effect on opinion formation based on the
majority rule and $q$-voter models on a complete graph. The external field can
be considered as the mass media in the social system, with the probability $p$
agents following the mass media opinion. Based on our Monte Carlo simulation,
the mass media effect is not strong enough to make the system reach a
homogeneous state (complete consensus) with the magnetization $m = 1$ for all
values of $p$, indicates that the existence of a usual phase transition for all
values of $p$. In the $q$-voter model, the mass media eliminates the usual
phase transition at $p \approx 0.21$. We obtain the model's critical point and
scaling parameters using the finite-size scaling analysis and obtain that both
models have the same scaling parameters. The external field effect decreases
both models' relaxation time and the relaxation time following the power-law
relation such as $\tau \sim N^{\beta}$, where $N$ is the population size, and
$\beta$ depends on the probability $p$. In the majority rule model, $\beta$
follows a linear relation, and in the $q$-voter model, $\beta$ follows a
power-law relation.
