For an endothermic reaction, energy of activation is $E_a$ and enthalpy of reaction is $\Delta H$ (both of these in $\text{kJ/mol}$). The minimum value of $E_a$ will be:

In an endothermic reaction, the energy of the products is higher than the energy of the reactants.The activation energy $E_a$ is the energy required to reach the transition state from the reactant level.
$$\Delta H=H_{\text{products}}-H_{\text{reactants}}$$
From the energy profile, it is clear that $E_a$ must be at least equal to $\Delta H$ plus the activation energy for the reverse reaction. Thus, $E_a>\Delta H$.