Use a random vector target, upon destination approach add a timer, then get a new random vector destination once the timer has run down. During the timer period you could even add special random animations.
How to call destinations for roaming AI, is explained here 7hw4o-d66Ys?t=1h4m9s (Begins marker 1h4m9s) - this tutorial explains how the AI is randomly walking, until it spots the player. Though, this can be modified ofc.