You can use velocity for this purpose. Also you can improvise your code if you have to have inputs through arrow keys and WASD.

Rigidbody _rb;
float _speed = 30f;
void Start ()
{
    _rb = GetComponent<Rigidbody> ();
}

void Update ()
{
    float horizontal = Input.GetAxis ("Horizontal");
    float vertical = Input.GetAxis ("Vertical");

    Vector3 fVelocity = new Vector3 (horizontal, 0, vertical) * _speed;
    _rb.velocity = fVelocity;
}

If you don't want to use WASD then use your code but change velocity instead of transform.position

You can use velocity for this purpose. Also you can improvise your code if you have to have inputs through arrow keys and WASD.

Rigidbody _rb;
float _speed = 30f;
void Start ()
{
    _rb = character.GetComponent<Rigidbody> ();
}

void Update ()
{
    float horizontal = Input.GetAxis ("Horizontal");
    float vertical = Input.GetAxis ("Vertical");

    Vector3 fVelocity = new Vector3 (horizontal, 0, vertical) * _speed;
    _rb.velocity = fVelocity;
}

If you don't want to use WASD then use your code but change velocity instead of transform.position