Generally, yes. The restrictions on contributions you can make to a retirement plan are applied to each employer separately. If you work for a company, the company is an employer. If you are self-employed, you are a separate employer, and can have a separate retirement plan for your business. But be careful. If both you and your employer establish some type of salary reduction plan, you might run up against an overall limit on contributions.
The most common types of salary reduction plans are 401(k) plans, tax-deferred annuity or 403(b) plans (these generally cover university professors and public school teachers), and 457 plans (sponsored by state and local governments and other tax-exempt organizations). A SIMPLE IRA is also a salary reduction plan.
Although the amount of your salary or compensation you can defer into each of these plans is limited, the law also puts a limit on the total amount you can defer into all such plans, if you happen to be covered by more than one. The overall limit depends on the type of plan you participate in.