No, it is not ok to do that. Because the light resource is too strong and near which cause the eye nerves to get tired easily, our eyes may get the images in the corneal with no reaction. If you do this often, your eyes may get short sighted or let the formal prescription get higher.
I strong recommend you not do this again. It is bad for your eyes when you read books with flashlight in the dark, Maybe in short time, you can't realize it. But if you do this last for a long time. It will make your eyes nearsighted or make your nearsightedness more seriously. So, If you want to read your looks, just do it in bright place.
It is not ok to do that. First of all, I must point out that reading books with a flashlight in the dark has do great harm to your eyes. A flashlight can't provide you with enough light for you to read in the dark. So you must get close to the book in order to look clear. That will make your eyes feel exhausted and decline your eyesight as a result. If you use LED Flashlight torch, you should ban using it to read in the dark. Because the light from LED belongs to cold light and it will reflect light. Reflecting light means light will get into our eyes which will harm our eyes. At last I advise you to use reading lamp or 60w incandescent lamp or 15w fluorescent lamp.