Steve's answer is right (IMHO).
BDD test frameworks, like Cucumber, Lettuce/Behave, JBehave, SpecFlow, etc., provide a separate textual test description,
which can be executed with a thin test automation layer (which interacts with your system/software under test).
This textual description is often easy to grasp even for non-technical people and provides an (up-to-date) documentation of the system behavior.
Therefore, it often serves as documentation with examples that describes how the system/software behaves.
In general, these tests are also more abstract (=> as acceptance tests) and provide a more high-level view on your software/system.
Sometimes you can add tests without need to extend the test automation layer.
If this aspect (separation between textual test and test automation) is not important you (and you are more productive), you can also use your current test framework.
Note that there are by now also BDD tools that provide a middle way:
You program like in a normal test framework, and the output is readable text (Given/When/Then or other styles).