Requirements Engineering (RE) discipline deals with elicitation, analysis, specification, validation and management of requirements. Several ontology-driven approaches have been proposed to improve these RE activities. However, the requirements engineering community still lacks a comprehensive understanding on how ontologies are used in RE process. The objective of this work is to explore how ontologies are employed in requirements engineering, aiming to identify the main phases addressed, the languages that have been used, the types of existing contributions, as well as the requirements modeling styles have been used and the benefits of using ontology in RE. We conducted a systematic literature review to identify the primary studies on the use of ontologies in RE, following a pre-defined review protocol. Sixty-six papers were selected, covering the five main RE process phases. Moreover, we have identified thirteen ontology-related languages. Furthermore, twenty-six empirical studies have been identified which provided evidence of five group of benefits. The main findings of this review are: (1) there are empirical evidences to state that ontologies benefit RE activities in both academy and industry settings, helping to reduce ambiguity, inconsistency and incompleteness of requirements; (2) the vast majority of papers do not meet all RE phases; (3) nearly half of the papers use W3C recommended languages; (4) the majority of contributions are supported by a tool; and (5) there is a great diversity of requirements modeling styles supported by ontologies.