AIBrain.cs

using UnityEngine;
using UnityEngine.AI;

public class AIBrain : CharacterBrain
{
    public AIBrain(NavMeshAgent navMeshAgent) : base(navMeshAgent)
    {
        navMeshAgent.GetComponent<Renderer>().material.color = Color.white;
    }

    public override void Tick()
    {
        if (!navMeshAgent.hasPath || navMeshAgent.pathStatus != NavMeshPathStatus.PathComplete)
        {
            Vector3 position = GetRandomPosition();
            navMeshAgent.SetDestination(position);
        }
    }

    private Vector3 GetRandomPosition()
    {
        var randomOffset = new Vector3(
            UnityEngine.Random.Range(-5f, 5f),
            0f,
            UnityEngine.Random.Range(-5f, 5f));

        return navMeshAgent.transform.position + randomOffset;
    }
}