If you are seeing jobs being advertised in newspapers, company websites, and other locations then companies are looking. Yes some business and industries have slow periods for hiring; but many do not.
Some organizations also use the winter months to prepare for hiring college students in the summer for paid or unpaid internships. If you wait till the spring you may be too late.
Some companies plan hires in response to growing their business and may link it to their planning cycle. But that cycle can take place at any time during the calendar year. Others base their hiring on winning new contracts so they have no direct link to the calendar.