There is no biblical evidence that the devil can read our minds.  Knowing our thoughts is only attributed to God, never anyone else.

• 1 Chron. 21:8, "for the Lord searches all hearts, and understands every intent of the thoughts."
• Psalm 94:11, "The Lord knows the thoughts of man, that they are a mere breath."
• Matt. 9:4Matt. 9:4, "And Jesus knowing their thoughts said, 'Why are you thinking evil in your hearts?'"
• Matt. 12:25, "And knowing their thoughts He [Jesus] said to them, ?Any kingdom divided against itself is laid waste; and any city or house divided against itself shall not stand."

    So, when you are praying, do not worry if the enemy can ready your mind.  Trust the Lord that He alone can read your thoughts.