Not, exactly, no.

Atheism is simply not believing in any gods, whereas secularism is the practice of keeping religion/theism separate from government, or other things.

Secularism is not a promotion of atheism, but rather, a position of complete neutrality on the topic of religion. [1]

Think of the public roads. They don't promote religion, nor do they hinder it, nor do they promote being non-religious, nor do they even have anything to say on whether religious beliefs are established in evidence or not. They're simply roads that anyone, of any religion (or not), can drive, and get to where they're going.

This is the state that secularists want to maintain for the whole of government, maximizing freedom and fairness for everyone, equally.

Examples of non-secular atheistic governments would be Stalin's Soviet Union, or Mao's China. Secular nations place no requirements on their constituents on what they believe religiously, by definition, and thus, is better for free thought and expression.

Many secularists are religious and theistic. Reverend Barry Lynn is the Executive Directory of Americans United for the Separation of Church and State, and is also a religious leader [2]. Secularism and theism are not mutually exclusive.