In the dual L ^{\Phi^* of a \Delta_2-Orlicz space L ^\Phi, we show that a proper (resp. finite) convex function is lower semicontinuous (resp. continuous) for the Mackey topology \tau(L ^{\Phi^*,L^\Phi} ,L_\Phi} ) if and only if on each order interval [-\zeta,\zeta]=\{\xi: -\zeta\leq \xi\leq\zeta\} (\zeta\in L ^{\Phi^* ), it is lower semicontinuous (resp. continuous) for the topology of convergence in probability. For this purpose, we provide the following Koml\'os type result: every norm bounded sequence (\xi_n)_n in L ^{\Phi^* admits a sequence of forward convex combinations %DIFDELCMD < \xi%%% \bar _n\inconv(\xi_n,n+1,...) such that \sup_n| %DIFDELCMD < \xi%%% \bar _n|\in L ^{\Phi^* and }%DIFDELCMD < \bar{\xi}%%%  and }\bar _n converges a.s.
In the dual L _{\Phi^* of a \Delta_2-Orlicz space L _\Phi, that we call a dual Orlicz space, we show that a proper (resp. finite) convex function is lower semicontinuous (resp. continuous) for the Mackey topology \tau(L ,L^\Phi} _{\Phi^*,L_\Phi} ) if and only if on each order interval [-\zeta,\zeta]=\{\xi: -\zeta\leq \xi\leq\zeta\} (\zeta\in L _{\Phi^* ), it is lower semicontinuous (resp. continuous) for the topology of convergence in probability. For this purpose, we provide the following Koml\'os type result: every norm bounded sequence (\xi_n)_n in L _{\Phi^* admits a sequence of forward convex combinations %DIFDELCMD < \xi%%% \bar\xi _n\inconv(\xi_n,n+1,...) such that \sup_n| %DIFDELCMD < \xi%%% \bar\xi _n|\in L and }%DIFDELCMD < \bar{\xi}%%% _{\Phi^* and }\bar\xi _n converges a.s.
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