No, it isn’t true. I’ve known many men and women who were deeply committed to Christ but were also active in various levels of politics.
In fact, I wish more Christians would get involved in politics, because our world needs leaders who believe in right and wrong, and know they are accountable to God for all they do. The Bible is full of examples of men and women who gave leadership to their people, and yet did not compromise their moral and spiritual convictions. Joseph, for example, was appointed prime minister of Egypt not only because of his wisdom, but because he refused to compromise his moral integrity (see Genesis 39-41).
At the same time, politics–like any other career–has its own set of temptations and pressures, and you need to face them honestly. Some people, for example, enter politics solely out of pride; they enjoy the attention, or they like to have power over others. Others sacrifice their moral principles in order to gain position or stay in office. Don’t let this be true of you.
No matter what the future holds, however, make it your goal above all to live for Christ and seek His will for your life. Let Jesus’ command be your guide: “But seek first his kingdom and his righteousness” (Matthew 6:33). Yes, someday God may give you a position of leadership–but whether He does or not, submit your life to the greatest leader of all: the Lord Jesus Christ.