This is a great question, and being a bloke, I sub-contracted out to my wife on this one, so much of what I’ve written here is based on a conversation I had with her.
The short answer is" maybe.
Here’s what I mean.
Let’s just think for a minute about sex in general. The Bible tells us that sex is good, and that’s it’s good for marriage. As you may well know, sex is created by God for a husband and a wife to enjoy in their marriage - and it’s something that is good for their relationship, since having it in your marriage is part of God’s plan for bonding you and giving you a healthy relationship.
Remember Genesis 2:24-25:
The image of ‘one flesh’ is a sexual one. The husband and the wife ‘become one’ as they are married and have sex with one another. And in this pre-Fall situation, there is no shame in being naked - they are totally open with each other, and comfortable with each other.
At the point where God joins this man and woman then, he talks about sex. It’s good, in the sense that it’s a fundamental part of God’s design for marriage, and marriage isn’t going to work as well if it’s not happening. We know from relationship studies that regular sex in a marriage relationship is good for the marriage itself, and for the well-being and fulfilment (and security) of each person in the marriage.
That’s the first thing. Having that in mind, it’s probably worth considering why the question has come up for you. Is it because of a lack of desire on your part that this issue has come up? If that’s the case, it would be worth thinking through why that might be - not to find something or someone to blame, just to know yourself and what’s going on in your heart and mind better. For example, is there something in your relationship with your husband that is ‘short-circuiting’ your desire? Do you resent him in some way, or feel that he resents you? Is there something unresolved that you might not think about consciously, but could be affecting your sexual desire for him?
Or perhaps you’re chronically tired or stressed. Either of these (and many others things) could mean that you just find it really hard to get excited about sex, or at least sex at the frequency your husband seems to want. Maybe you’re still suffering the effects of some past trauma in your relationship or another relationship? I don’t know, but it’s worth reflecting on these things - only you know yourself this well - and working out whether there is something that’s making it hard to want to have sex with your husband.
In terms of actually answering your question directly (finally!), the Bible does speak about saying ‘no’ to sex.
1 Corinthians 7:3-5:
The apostle Paul is speaking here in the context of what I mentioned above: that sex is part of marriage - it’s part of the way God designed marriage to work. And so marriage ceases to work as it’s designed if one person denies the other person sex. That’s why Paul says,"Do not deprive on another, except perhaps by agreement…" Paul’s priority is to encourage good marriages, in which the husband and the wife are servants of one another. And I can tell that you want to do what’s right, because you asked as"a good Christian wife". So you’re heading in the right direction.
Having said that, there may be legitimate reasons for not having sex. Perhaps you can’t bear the thought of it, because you’ve just had a baby, perhaps you’re unwell, perhaps it’s something else. If this is the case, one of the most important things you can do it talk about it with your husband. Tell him what you’re thinking and try to explain what’s going on for you. He will appreciate this much more than you giving him a hint that you’re not interested in sex tonight.
Remember that God wants us to examine our motives (think of Jesus’ words about what goes on in the heart in the Sermon on the Mount in Matthew 5). You are the only one who knows what’s in your heart, so reflect on the purpose of sex in marriage, and Paul’s word about each person having authority over the other’s body and not denying each other, and work out whether you have some valid reason for not having sex at this time, or whether you need to repent and work hard to be a better servant to your husband. Or maybe it’s a bit of both.
Above all, continue to pray to God that he would work in you by his Spirit, to make you servant-hearted and give you good knowledge of yourself and your motives. He’s a good God and he wants our marriages to work!
I hope that answers your question.
Some resources that might help: