const ascene = AFRAME.scenes[0]
const scene  = ascene.object3D
const object = new THREE.Mesh(
	new THREE.BoxGeometry(1, 1, 1),
	new THREE.MeshBasicMaterial({ color: 0xff0000 })
);
object.position.set(0.3, 1.4, -0.4)
object.scale.set(0.2,0.2,0.2)

// instead of animate() we use onAfterRender 
// (or monkeypatch AFRAME.scenes[0].renderer.render() for full-control)
object.onAfterRender = () => object.rotation.x += 0.01

scene.add(object);