My firm belief is that the enemy cannot read our minds. But, two things:
1) The enemy becomes expert at reading our face, our body language, our emotional responses, our voice, our gestures, etc, etc... You get it. If the devil wants to hinder someone, he will examine them closely and use whatever insight he can glean from those observations. He is brilliant, and he also watches our environments and knows how and when to push buttons or place little whispers into our mind to deceive or demoralize.
2) The Bible clearly teaches that the heart, above all things, is wickedly deceptive. From that passage, I presume the heart to translate into our flesh. Christians can be walking after the Holy Spirit or tarrying in their flesh. In other words, New Covenant believers can walk powerfully after the Holy Spirit if they live their faith according to Biblical standards and practices. But, if people don't walk out those things daily, they can get very fleshly and carnal. In that state, our hearts will whisper deceptive nonsense to us. Why? Because our flesh, as the Bible clearly states, is the enemy of God even though we've surrendered our lives to Him.
There have been times when I've been walking so powerfully after the Holy Spirit that my flesh was silent. Then, when I heard from the Holy Spirit, I knew it. It was very clear.
If you want to walk after the Spirit in a greater measure, mortify the flesh through fasting and prayer. Spend time in worship and study of the Word. You can gain a great deal of momentum as it's kind of like getting a two-ton truck rolling.