No, it is not.
This accusation arises frequently from those theists who want to make atheists seem like hypocrites or fools.
You guys bash on religion so much, but you are a religion! Hah!
Technically, one can have a religion with no gods, but that does not mean that having no gods makes one a religion.
re•li•gion (Excerpt from Dictionary.com)
- a set of beliefs concerning the cause, nature, and purpose of the universe, esp. when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
- a specific fundamental set of beliefs and practices generally agreed upon by a number of persons or sects: the Christian religion; the Buddhist religion.
- the body of persons adhering to a particular set of beliefs and practices: a world council of religions.
- the life or state of a monk, nun, etc.: to enter religion.
- the practice of religious beliefs; ritual observance of faith.
- something one believes in and follows devotedly; a point or matter of ethics or conscience: to make a religion of fighting prejudice.
- religions, Archaic . religious rites.
- Archaic . strict faithfulness; devotion: a religion to one's vow.
Atheism (standard) itself does not adhere to any of these above points. Atheism has no doctrine, no dogma, no rituals, no devotion, no beliefs in anything supernatural, no standard philosophy. Atheism does not provide any answers to life or philosophy, or even political views. The one and only thing that all atheists agree on is that none of them believe in a god.
Keep in mind that not all these different types of religions are the same. We would not equate a devoted football fan to Catholicism, for instance. Atheists aren't denouncing anything that starts with the dreaded "R-word", either. Only particular attributes of the regular concept of religion are what atheists tend to object to.
When atheists "bash" on religions, what they are objecting to is a large group of people enacting mass action based on delusional beliefs, often causing mass harm.
We don't object to them forming groups.
We don't object to them socializing.
We don't object to them having common opinions.
We don't object to them having common activities.
We don't even really object to them proselytizing (outside of inappropriate or annoying situations).
We prefer people derived their beliefs from reality, not from superstition. Delusion-based beliefs generate problems that compound when a religion essentially indoctrinates and brainwashes millions upon untold millions of people with these beliefs. Beliefs inform one's actions, thus, having incorrect beliefs can lead one to take mistaken actions. Multiplying this effect on a massive scale can generate incredible amounts of harm.
There's a reason why atheists don't spend a lot of time denouncing Buddhism - because they aren't causing trouble, as far as we are aware.