Sometimes my eye goes out of focus and zooms back into focus. Is there something wrong? Is this normal?

No. This is the physiologic process of accommodation. Thus you can control your focal point to be near or far. However, if you are always blurred or experiencing eye strain, or have any other sustained visual problem, then you should have it checked out. Around age 40s, presbyopia or loss of accommodation can sometimes be noticed.
Normal. This is normal. Especially if it occurs between shifting from distance viewing to near viewing. Different focus mechanisms are employed for each function and there may be a delayed response while making the transition. If this occurs mainly at either viewing depth, perhaps you need spectacle correction.